Quick Summary (TL;DR)
The best multi-zone heating system is not the one with the most smart relays. It is the one whose manifold, room controls, actuator outputs, pumps and heat-source demand signals are designed as one hydraulic and electrical system. A room thermostat requests heat; the zone controller operates the appropriate manifold actuators; the wiring centre or approved controller coordinates pumps and the boiler or heat pump; the heating appliance retains all its own protection functions. Home Assistant is most reliable as a supervisory layer for temperatures, schedules, telemetry and user interfaces rather than as the only device standing between a closed manifold and a running circulator.
For a straightforward radiator system, individual smart thermostatic radiator valves (TRVs) can make sense. For a wet underfloor heating (UFH) manifold serving several rooms, buy a purpose-built controller that explicitly supports your actuator voltage (often 230 V AC or 24 V AC), contact type, actuator quantity, room/channel mapping, source interface, pump control and heating/cooling strategy. “Eight zones” is not the same as “eight loops”: one room can have multiple loops and multiple actuators driven together. Check the controller’s total loading as well as its per-channel rating.
For heat pumps, minimum water flow, minimum active heating volume, weather compensation and defrost water circulation usually matter more than rapid room-by-room switching. Close every valve at the wrong time and you can create poor performance or an equipment fault. Do not improvise a bypass, force a pump or disable flow checks; the hydraulic design must comply with the exact heat-pump manufacturer’s commissioning instructions. For gas boilers, oversized output relative to the smallest active zone can cause repeated burner cycling even though the thermostat wiring is electrically correct.
Practical shortlist: Heatmiser’s correctly matched 230 V wiring-centre ecosystem where standard 230 V thermostats and actuators are used; Danfoss Icon2 with its specified 24 V actuators when a coordinated proprietary floor-heating controller is wanted; SALUS KL-series variants selected for the exact voltage and region; and Uponor Smatrix controllers for systems designed around Uponor’s specified actuators and room controls. None is a generic interchangeable relay board. Manufacturer specifications, integration details and availability vary by variant and country.
An ESP32AliExpress price with ESPHome can be an excellent monitor or non-safety supervisory interface. We already cover its physical controller architecture in our ESP32 multi-zone heating controller build; this buying guide intentionally concentrates on selecting and commissioning professional wet-heating components instead of duplicating those wiring instructions.
Understand the four different meanings of a heating zone
Sales listings regularly confuse rooms, control zones, water loops, and electrical actuator channels. The difference is the starting point of a reliable specification. A 28 m² open-plan room may need three heating loops to meet pipe-length and pressure-drop constraints but still be one temperature-control zone. An adjacent bathroom could be a separate zone with only one loop. A manifold can have twelve outlets while the thermostat wiring centre needs only seven independently controlled room channels; however its seven channels must collectively drive all twelve connected actuators within the manufacturer’s electrical limits.
| Term | Meaning | Example in a house | Buying implication |
|---|---|---|---|
| Room | Architectural space that needs a comfort target | Kitchen, study, bedroom | Number of thermostats or sensing locations may follow occupied rooms |
| Control zone | Set of emitters following one temperature request | Open-plan kitchen/living space | Controller must support enough independent demands |
| Manifold loop | One physical circuit of underfloor pipe | Three loops in a large living room | Manifold needs one supply/return port pair per loop |
| Thermal actuator | Motor/wax device on a manifold valve | One actuator per return-valve position | Need correct voltage, thread/stroke and sufficient output capacity |
| Electrical output/channel | Controller’s independently switched output | One channel drives three living-room actuators | Must check simultaneous current/inrush and stated actuator count |
| Heat-source enable | Demand sent towards boiler or heat-pump controller | Isolated relay or approved input | Signal interface does not replace water flow protection |
| Hydraulic zone | Circuit with distinct pump/mixing/temperature requirements | Radiator circuit versus UFH circuit | May need a separate pump group and hydraulic design |
Write a schedule mapping room → thermostat → controller channel → actuator(s) → manifold loop(s) → physical pipe run. Photograph and label both manifolds and all actuators before closing service panels. A room/loop error can produce a perfectly functional dashboard that warms the wrong room, a particularly frustrating fault after flooring is complete.
Example: why a 12-loop manifold does not require 12 thermostats
Consider a floor with eight occupied rooms: the living room has three loops; the kitchen two; the principal bedroom two; and five additional rooms one each. That is twelve loops but eight control zones. A wiring centre with eight independently controlled channels might accommodate the job if it allows the necessary number of actuators on the living-room and kitchen channels. But an eight-channel product with eight total actuator outputs may not. Some controllers have a channel count, a maximum total actuator count and a maximum load per channel: all three figures must be checked.
Even when a manufacturer says “up to six actuators per zone”, do not assume every zone can simultaneously drive six actuators without also satisfying a board-wide total-load constraint. Verify the exact version of the wiring centre, the actuator data sheet, the fuse requirements and the permitted cable installation method. There is no universal “plug them all into any terminal” rule.
The hardware stack: what each component is responsible for
A reliable system has four distinct layers. First is the hydraulic layer: heat source, pumps, mixing devices, distribution pipework, manifolds, isolation valves, strainers and safety provisions. Second is the actuation layer: thermal heads or motorised valves that admit or restrict flow to emitter circuits. Third is the control layer: wall thermostats, controllers and wiring centres that decide which heads open and whether to request heat. Fourth is the supervision layer: Home Assistant, energy monitoring, reporting and optional schedules. Designing them in reverse order—from an attractive app screenshot backwards—usually creates avoidable complexity.
| Component | Essential job | Specify before purchase | Frequent mismatch |
|---|---|---|---|
| Flow/return manifold | Distribute water among loops; provide isolation/balancing | Port count, flow range, fitting size, actuator valve thread | Twelve loops but only eight outlets |
| Flow meterAliExpress price / balancing valve | Set individual loop flows | Meter range, design flow per loop, operating position | All meters opened fully without balancing |
| Thermal actuator | Open or close a branch valve | 24 V/230 V, AC/DC if relevant, NC/NO, connection and stroke | 24 V head connected to a 230 V output |
| Wiring centre | Distribute control power and aggregate demand | Channels, loads, compatible stats, pump and boiler outputs | Interpreting ‘volt-free’ as supplying power |
| Room thermostat | Measure ambient and generate heat demand | Sensor placement, compatibility, cooling support | Wall sensor behind a curtain or in direct sun |
| Floor probe | Limit floor temperature when required | Sensor type/length and controller support | No floor-limit logic below vulnerable finishes |
| Mixing group | Deliver a lower UFH water temperature if designed | Heat-source temperatures, pump sizing, mixing control | High-temperature feed entering an unsuitable floor loop |
| System circulation pump | Maintain designed flow | Head/flow curve, operating logic, wiring interface | Relay turns pump off during manufacturer-required overrun |
| Heat-source interface | Communicate heating demand | Approved dry contact, bus or manufacturer-specific control | Mains voltage fed into low-voltage input |
| Home Assistant integration | Monitoring and optional setpoint scheduling | Local/remote API, supported entities and offline behaviour | Cloud failure stops a critical source-demand path |
Manifold buying guide: ports, loops, flow meters and serviceability
Wet UFH manifolds often arrive as attractive stainless-steel or brass bars equipped with flow meters and manual valve caps. Quality differences are not just cosmetic. Look at the documented permitted pressure/temperature, fitting standard, replacement seals, fill and purge arrangement, flow-meter range and access for service. Some manifolds offer valves ready for electrothermal heads. Others need adapter collars or have proprietary actuators. Compatibility with a generic M30 × 1.5 body cannot be guessed from the external appearance of a white plastic cap: stroke, valve-closing force and thread requirements all matter.
Count loop outlets using the actual pipe layout, not only the number of rooms. Pipe spacing, pipe diameter, heated area and acceptable circuit length influence loop count and design flow; those are design-engineer decisions, not universal “square metres per loop” promises. Leave service access around flow meters, bleed points and actuator cables. Allow space for a wiring centre, cable routing, strain relief and any future inspection required by the installation manual.
Manifold design checklist
| Question | Why it matters | Evidence to request |
|---|---|---|
| How many complete pipe loops? | Each generally needs a supply and return manifold connection | As-built pipe/loop drawing |
| What is design flow per loop? | Flow meters must cover the correct measuring range | Heat-loss and hydraulic balancing schedule |
| What is the maximum circuit pressure loss? | Pump must overcome manifold, valve and pipe resistance | Designer’s head/flow calculation |
| Are thermal actuators supported? | Manual valve bodies may need compatible adapters | Manufacturer’s compatible actuator list |
| Which threads and stroke? | Physical fit is insufficient if valve does not travel correctly | Valve and actuator data sheets |
| How are loops filled and purged? | Trapped air can prevent circulation | Fill/drain valve arrangement and commissioning process |
| Is there suitable access? | Flow meters and heads eventually need service | Manifold cupboard clearance/photographs |
| Is water temperature limited? | Floor finishes and occupants have exposure limits | Design supply-temperature and floor-limit controls |
Flow balancing and small-room comfort
An unbalanced manifold may send too much water through short loops while starved long loops warm slowly. The resulting room-temperature difference can look like a thermostat problem, especially when a dashboard displays every zone as demanding heat. Balance the circuits against their specified design flow, with the required system operating conditions and according to the manifold instructions. Do not assume each flow meterAliExpress price should show the same number: pipe lengths and room loads differ.
When a single small room calls for heat, the system’s total flow requirement may not be met by that one circuit. A minimum-flow strategy belongs in the hydraulic design, not in an automation that simply commands every fourth valve to remain open. A permanently open circuit, differential bypass, low-loss header, buffer or hydraulically separated pump group can each change system behaviour; the appropriate arrangement is determined by the appliance, pump and emitter design. A bypass that merely circulates hot water around a heat pump without adequate active water volume may protect flow while still harming efficiency or defrost performance.
24 V versus 230 V actuators: an electrical compatibility problem, not a preference
The head that moves a UFH valve is commonly an electrothermal actuator: power heats a small element and the device gradually changes position. Most applications use normally closed (NC) heads, closed without control power and opened when energised, but normally open (NO) models exist. Both can be appropriate depending on the controller and failure philosophy. The response may take minutes. That is normal for thermal wax drives and is one reason rapid pulse-width switching like an electrical motor is inappropriate unless the controller explicitly supports the actuator with its own designed timing method.
Voltage is non-negotiable. A nominal 24 V head must never be wired to a 230 V controller output, and a 230 V head will not operate correctly from a 24 V controller. Note the distinction between 24 V AC, 24 V DC and controllers that explicitly permit both; do not infer support from the number alone. Controller supply voltage can also differ from its actuator output voltage. For example, an appliance can take 230 V mains power while producing regulated 24 V actuator outputs.
| Characteristic | Common 24 V actuator arrangement | Common 230 V actuator arrangement |
|---|---|---|
| Typical environment | Dedicated low-voltage UFH controller ecosystem | Mains-rated wiring centre with 230 V outputs |
| Power supplyAliExpress price | Controller/transformer rating must cover all heads | Mains wiring and protective measures required |
| Thermostat compatibility | May use low-voltage proprietary/wired bus | May use line-voltage compatible thermostats |
| NC versus NO | Available; controller must be configured properly | Available; controller must be configured properly |
| Wiring approach | Cable sizing, isolation and SELV/PELV rules apply | Qualified installation and appropriate enclosures |
| High-level advantage | Separation of valve drive from mains at heads where properly designed | Readily available within some conventional wiring-centre systems |
| Common purchasing mistake | Assuming a 24 V DC supply works with 24 V AC-only heads | Connecting to a low-voltage or dry-contact-only control output |
How to calculate a zone’s actuator load
A zone with four actuators rated 2 W each has an illustrative steady-state total of 8 W, excluding controller overhead: 4 × 2 W = 8 W. At 24 V the idealised steady-state current is roughly 8 W / 24 V = 0.33 A. At 230 V, eight watts is about 0.035 A at unity power factor. Neither arithmetic result is enough to select wiring and protection: start-up current, inrush characteristics, operating voltage tolerance, power factor, transformer capacity, terminal ratings, output thermal limits and manufacturer’s allowed head count remain decisive. The 24 V controller’s total rated output power might constrain the installation even if each zone individually appears small.
As a concrete example, Danfoss lists its Icon2 24 V main controller with 15 outputs, up to 15 compatible actuators and a stated maximum 2 W per output on a specified model; its mains supply is not permission to connect 230 V valve heads. Heatmiser describes 230 V actuators for its UH-series wiring centres and documents both per-zone and board-wide limits that vary by model. The correct conclusion is not that one voltage is superior; it is that buying mixed hardware without a full schedule is a costly mistake.
Normally closed, normally open and failure states
If the thermostat, wiring centre or network stops responding, what should happen to the actuator? NC normally closes when power is lost; NO normally opens. That says nothing by itself about the boiler, pump or heat pump response. The heating appliance has a separate safe shutdown, overrun and flow strategy. For instance, fitting NC heads throughout a heat-pump system without a suitable independent minimum-flow path can create a shutdown problem when every head returns to closed. Conversely, choosing NO heads to keep flow might create unintended overheating in a room unless the entire scheme is designed for that state.
| Failure or change | Expected behaviour to verify | Why it must be tested |
|---|---|---|
| Power fails at wiring centre | Heads move toward their physical unpowered state | NC/NO assumptions are often undocumented |
| Thermostat loses battery/radio link | Controller’s local timeout/fallback applies | Some controllers maintain last demand; others stop |
| Wi-Fi / Home Assistant unavailable | Essential heating still follows approved local controls | Avoid software as sole protective link |
| Actuator cable open circuit | That loop may stay closed despite demand | LED ‘heat on’ is not proof of water flow |
| Boiler or heat-pump lockout | Source remains off; pump/valves follow manufacturer’s logic | No controller should bypass appliance protections |
| Controller restart | Outputs return to documented start state | Boot-up energisation can surprise system designers |
| Summer cooling mode | Dew-point/condensation protection remains effective | Cooling through UFH needs specific limits |
Wiring centres versus standalone relays versus integrated controllers
A wiring centre is not merely a tidier junction box. In a correctly designed system it can aggregate multiple room demands, energise relevant actuators and provide separate outputs for manifold pump, zone valve and heat-source enable. Models differ: some support timed opening delays, pump exercise, changeover, radiator/UFH distinctions, cooling inputs or dew-point interlocks. These features become important in systems where a boiler reacts faster than wax actuators physically open.
A bank of eight smart Wi-Fi relays may appear cheaper on a shopping page, but it does not inherently implement any of those functions. Relay boards also vary in electrical isolation, contact ratings, leakage, enclosure approval, watchdogs and commissioning documentation. A controller specifically designed for wet heating is usually the safer choice for permanent fixed installation. Home Assistant can then adjust thermostats or collect data through a supported interface.
| Architecture | Best-fit installation | What it does well | Major caveat |
|---|---|---|---|
| Wired 230 V wiring centre | Conventional UFH with matching thermostats and heads | Centralised, clear physical connections | Mains wiring and model-specific load limits |
| 24 V integrated zone controller | Coordinated low-voltage actuator ecosystem | Matched control, balancing and scheduling options | Generally proprietary component compatibility |
| Wireless thermostat + receiver/centre | Retrofit without room-stat cable | Less disruptive room control | Battery, RF coverage and pairing matter |
| Smart TRVs on radiators | Existing hydronic radiators | Little manifold work for per-radiator control | May not coordinate boiler demand or minimum flow |
| Separate certified zone relays | A specific compatible control extension | Flexible discrete signals | More integration and failure-mode design needed |
| DIY ESP32AliExpress price/ESPHome switch bank | Laboratory/test rig; supervisory signals via rated interface | Detailed local telemetry and custom logic | Not a replacement for protected fixed wiring and heat-source interlocks |
Pump and boiler outputs have different meanings
A volt-free relay contact is an isolated switch contact: it does not automatically supply power. A switched-live output supplies or switches a line-voltage conductor as documented. A digital heating bus conveys messages rather than a binary electrical contact. Connecting these interchangeably can damage the appliance or create dangerous mains exposure. Always match the exact boiler or heat-pump input described in its manufacturer wiring schematic. An OpenTherm terminal is not a universal place to attach an ordinary relay, and a Modbus port is not a thermostat terminal.
The controller may need to delay enabling the heating source until manifold actuators have begun to open. It may also need a specific pump-overrun arrangement after heat demand ends. Those delays and interlocks are not universal values; a controller’s built-in function must be configured using its instructions and the heat-source commissioning data. A wall thermostat’s ‘off’ decision should not casually remove power from a circulator whose continued operation the heat-source manufacturer requires.
For a broader protocol comparison, see OpenTherm Gateway with ESP32 and Home Assistant and the queued companion article OpenTherm vs Modbus vs Dry Contact: Heating Control Protocols Explained. A protocol label alone does not prove the accessory offers independent local Home Assistant control.
Manufacturer ecosystem comparison: Heatmiser, Danfoss, SALUS and Uponor
Each family contains multiple generations. The names below illustrate verified design differences, not a universal price ranking or guarantee that every model has a native Home Assistant integration. Specifications and compatible accessories must be checked again at the time of purchase. Do not treat a Zigbee radio inside a proprietary heating system as proof that an ordinary Zigbee coordinator can adopt and control every function.
| Example hardware | Published physical/control characteristics | Appropriate buyer | Verify before ordering |
|---|---|---|---|
| Heatmiser UH8 | Eight-zone 230 V thermostat/wiring centre; documented heat-source volt-free interface and UFH pump/valve outputs | Wired UFH designed around compatible 230 V heads | Exact UH8 version, live/neutral terminals, zone 8 mode, head count, total board load |
| Heatmiser UH8-RF v2 | Wireless thermostat ecosystem, 230 V actuator outputs, per-zone configuration options | Retrofit where room cables are difficult | Required thermostat generation, radio receiver, local/app integration path |
| Danfoss Icon2 Basic/Advanced 24 V | Documented 24 V valve outputs, up to 15 outputs for cited part numbers; pump/boiler relays | System designed around 24 V Danfoss controls | Product code, 2 W/output limit, supply-temperature-control version, cloud/local bridge |
| SALUS KL08RF | Eight-zone wireless wiring centre in 230 V actuator ecosystem; model variants | SALUS ecosystem retrofit | Exact regional variant, whether ’24V’ version is required, interface to HA |
| SALUS KL08RF24V | Variant with 24 V actuator outputs and published up-to-three-actuators-per-zone description | Explicitly specified 24 V arrangement | Supply/output details against manual: product snippets can mix rating terminology |
| Uponor Smatrix Base Pulse X-245 | Manufacturer documents 24 V AC Uponor actuators, six channels and up to eight actuators for the base controller | New installation designed as complete Uponor system | Additional channel modules, gateway/services for app and integration, room-bypass design |
| Professionally designed separate zone relays | Depends entirely on selected approved relay and pump/heating input | Bespoke nonstandard zoned retrofit | Isolation, electrical drawings, protections, serviceability, local fallback |
What not to infer: ‘Zigbee’ is not shorthand for direct Zigbee2MQTT or ZHA compatibility; ‘wireless’ does not mean cloud; and ‘app supported’ does not mean Home Assistant exposes pump-level controls. Before buying ten thermostats, verify the precise actuator, controller and thermostat pairing from an official compatibility matrix. Models such as Danfoss Icon2 can have Basic and Advanced subtypes with different water-temperature support even when actuator-voltage ratings are similar.
A practical shortlisting method
Start with the hydraulic designer’s confirmed number of loops, design flow rates, flow temperatures and heat-source type. Next establish whether the installation calls for 24 V or 230 V actuators and whether those heads are already on site. Filter controllers by documented output voltage, channels, number of actuator heads, pump output and permitted heat-source-demand connection. Only then compare thermostat aesthetics, mobile apps, cloud accounts and Home Assistant features. A £30 saving on a controller is not useful if it forces replacement of twelve valve heads or deprives the heat pump of required hydraulic flow.
Heat pump zoning: the minimum-flow problem
Heat pumps work most efficiently when they can deliver heat at a stable, relatively low water temperature with suitable circulation and long operating periods. An installation with many room thermostats that repeatedly close loops can reduce active water volume, increase return temperature transients and interrupt steady operation. The heat pump’s controller should usually retain authority over compressor protection, defrost sequencing and any required circulation. Weather compensation and modulation are often more consequential than aggressively switching eight floor zones on and off every few minutes.
A minimum flow requirement is a manufacturer-specific engineering limit, not an approximate percentage of valves to keep open. It may depend on operating mode, auxiliary heater operation and defrost. Consult the exact installer reference guide for flow and water volume requirements under all relevant conditions. For instance, Daikin’s manufacturer installation materials explicitly discuss minimum water flow and recirculation when all shut-off valves close; they are not permission to fit an arbitrary bypass to every heat pump.
| Configuration | Potential advantage | Risk if poorly designed | What the installer must confirm |
|---|---|---|---|
| Many independently closing floor loops | Room-specific temperature limits | Too little flow during low load/defrost | Minimum flow and volume at worst-case valve positions |
| Permanently available reference zone | Keeps one emitter path available | Single circuit may still be insufficient | Flow through that path and room comfort consequences |
| Differential pressure bypass | Maintains a recirculation path in some schemes | Short circuits water and can raise return temperature | Approved bypass position and setpoint; heat-pump requirements |
| Buffer tank / volumiser | Adds hydraulic volume where required | Heat losses and mixing may rise | Sizing, connection topology, pump control and stratification |
| Low-loss header / hydraulic separation | Decouples primary and secondary circuits | Mixing can reduce useful flow temperature or COP | Primary/secondary pump balance and temperature sensors |
| Modulated weather-compensated heat pump | Stable supply under broad conditions | Zones can still restrict physical circulation | Manufacturer-approved thermostat and hydraulic control strategy |
Why underfloor heating should not behave like a fast electric heater
A thick screed with embedded pipe may take hours to respond substantially to a setpoint change. A thermostat’s digital ON command does not heat the floor instantly; nor does turning it OFF instantly eliminate heat delivery from stored thermal mass. This is why room scheduling is generally better with modest setbacks and anticipation than with repeated short pulses. The appropriate schedule differs for low-mass retrofit panels and thick concrete slabs. For an energy forecasting approach, see Predicting Home Heating Demand from Outdoor Temperature and Thermal Lag once that companion article is published.
If the heat pump supports its own room controller and weather-compensation algorithm, it may be preferable to let that controller regulate supply water, with UFH thermostats providing comfort limits rather than frequently demanding complete compressor stops. The installer should document which device is the master demand authority and how floor temperatures and water-flow protection are handled when room setpoints are satisfied.
Boilers, radiator circuits and mixed-temperature installations
Gas boilers can also suffer when a small zone is the only one demanding heat. Suppose a modulating boiler’s lowest stable space-heating output is 5 kW while an individual small bathroom requires 0.4 kW at that moment. Without adequate water volume and compatible control, the boiler may satisfy the water-temperature limit rapidly and stop the burner, then repeat. This does not prove that the thermostat is wrong; it highlights a source-load mismatch. Observing burner state and water temperatures can help: our OpenTherm Gateway with ESP32 and Home Assistant explains possible telemetry, while the boiler’s safety controller remains authoritative.
Radiators and UFH may demand different water temperatures. A legacy radiator system might have been designed for much higher supply temperatures than a thick-screed UFH loop. Feeding both directly from one hot header with only thermostatic on/off valves does not magically provide the correct floor temperature. Depending on system design, a mixing group, separate controlled circuit, zone valve, hydraulic separator or revised radiator sizing might be appropriate. Do not assume every heat pump installation needs an extra mixing pump: some low-temperature heat-pump systems are designed for direct UFH supply.
| Installation | Distinctive design issue | Controller requirement |
|---|---|---|
| Boiler + floor-only wet UFH | Boiler supply can exceed suitable floor temperature | Designed mixing/supply limit plus source coordination |
| Heat pump + floor-only wet UFH | Minimum flow and slow emitter response | Heat-pump-approved hydraulic strategy and gradual zoning |
| Boiler + radiators + UFH | Different temperatures and fast/slow response | Separate radiator/UFH demand and safe flow paths |
| Heat pump + radiators + UFH | Radiator sizing vs low flow temperature | Validated heat-loss sizing and temperature zones |
| Heating and floor cooling | Condensation and surface comfort limits | Dew-point, humidity and changeover controls |
| Domestic hot water priority | Space heating may pause for cylinder heating | Equipment-native DHW priority; no relay conflict |
Heating/cooling changeover and condensation prevention
Cooling via water-filled floor loops is possible only with a system expressly designed for it. Floor surfaces must not be cooled to or below the dew point of the surrounding air. A temperature probe alone, or a general Home Assistant humidity reading in another room, is not an independent condensation safeguard. Many dedicated controllers offer dew-point inputs, floor limits, changeover configuration or manufacturer-specific humidity sensors. Their operating logic must be commissioned correctly. A floor controller that can heat well is not automatically cooling-ready.
The dew point changes quickly when windows open or occupancy raises humidity. A summer bedroom at 26°C and 65% relative humidity has a dew point in the high teens °C, so driving chilled water through an unprotected floor is hazardous. Use the manufacturer-approved controls and conservative supply constraints. Home Assistant may display dew-point trends and warn about sensor failures, but should not bypass hardware condensation protection or trigger unapproved cooling modes. Mixed radiator and floor circuits may also require separate changeover and insulation provisions.
Electrical relays, isolation and safety boundaries
There are at least four unrelated ratings to consider on a relay: coil/control voltage, contact working voltage, steady-state contact current and switching/inrush capability. A digital controller may provide only a low-current signal, not the electrical power for the attached pump. A manufacturer’s boiler-enable relay can have volt-free contacts that must be connected to a permitted external circuit, not to the appliance’s mains supply by guesswork. An output labelled 3 A is not automatically suitable for a 3 A inductive pump motor; the relay’s category and manufacturer’s documented application matter.
| Signal/device | Typical electrical nature | Recommended treatment |
|---|---|---|
| 24 V AC thermal head | Low-voltage powered actuator | Use compatible rated supply and correct controller output |
| 230 V AC thermal head | Mains-powered actuator | Qualified installer, rated wiring centre and enclosure |
| 230 V circulation pump | Mains inductive load | Approved pump output or appropriately rated contactor as specified |
| Volt-free boiler demand | Isolated contact provided by controller | Connect only to approved heat-enable terminals per boiler manual |
| Switched-live heat request | Line-voltage control | Never connect to dry-contact-only or bus terminal |
| OpenTherm/eBUS data | Manufacturer/protocol digital signalling | Use specified compatible interface, not raw relay contact |
| Heat-pump Modbus gateway | Serial/TCP communications | Read supported registers; restrict safety-critical writes |
| ESP32 GPIO | Logic-level output | Interface through approved isolated control device, not direct mains |
Mains work, manifold pump connections and gas appliance wiring must be done by suitably qualified installers following local electrical and gas regulations. Thermostats, switches and actuators should not share a cabinet simply because there is spare DIN-rail space; cable segregation, protection, ventilation and manufacturer enclosure rules apply. A mains distribution board or boiler’s service compartment is not a safe place for hobby jumper wires.
Why a DIY ESP32 board should not be the only heating controller
ESPHome provides excellent local sensors, status outputs and integration with Home Assistant. It even allows a switch to default OFF at boot. But software initialisation does not by itself establish a fault-safe electrical design. A stuck relay contact, welded contactor, GPIO glitch, loss of low-voltage power, Wi-Fi outage or corrupted configuration remains possible. Design normally requires independent hardware limits and the manufacturer’s controller to retain safety and circulation authority.
The sensible architecture is dedicated local heating controller first; ESP32/ESPHome for visibility, optional permitted setpoint interface or monitoring second. If an approved input specifically supports external demand or occupancy modes, an isolated dry-contact interface can sometimes be used—but only after the system designer confirms its electrical classification and how demand interacts with valve position, pump overrun and heat-pump minimum flow. See the existing ESP32 multi-zone controller project for the electronics concepts, not as a blanket certification for new fixed installations.
Home Assistant integration: choose a supervisory strategy
A good Home Assistant heating dashboard exposes room temperatures, target setpoints, actual thermostat operating modes, outdoor conditions, boiler/heat-pump operating status, water temperatures, pump status and alarms where supported. It should distinguish between a requested temperature and a confirmed physical state. A climate entity reporting heating may mean “thermostat requests heat”, not “boiler burner currently firing”. Similarly, a wiring-centre LED may indicate power to a thermal actuator, not proof that the valve has physically opened.
If the chosen ecosystem has a supported local integration, prefer it to screen-scraping a cloud app. If it has only a vendor cloud, assess API rate limits, future subscriptions, authentication, latency and offline behaviour. If it offers Matter/Thread or Zigbee transport, verify specific exposed capabilities through the actual bridge and firmware rather than equating protocols with complete thermostat support. Monitoring energy sensors is not the same as being able to command zone outputs.
A safe monitoring-only Home Assistant configuration
The following example assumes binary_sensor.ufh_heat_demand already represents a genuine upstream demand/status entity from an installed compliant controller. The example merely counts time with heating demand during the current day; it does not operate the pump, boiler or valves. Replace the entity with your actual device and ensure Recorder retains enough data for the requested interval.
# configuration.yaml — monitoring only; does not control heating power
sensor:
- platform: history_stats
name: UFH Heat Demand Hours Today
entity_id: binary_sensor.ufh_heat_demand
state: 'on'
type: time
start: '{{ today_at() }}'
end: '{{ now() }}'The result is demand time, not measured burner runtime or delivered heat. For actual runtime, monitor the appliance’s explicit burner/compressor state if provided. For consumed or delivered energy, use appropriate cumulative meters and the relevant Home Assistant energy and statistical integrations. A heating system’s zone demand can remain on while the heat pump defrosts, while a boiler waits through a lockout or while an actuator slowly opens.
Validate local integration and entity quality
| Question | Positive sign | Potential problem |
|---|---|---|
| Will room control function without internet? | Thermostats and centre retain local logic | Cloud service is required for daily heating |
| Does Home Assistant show current temperature? | Actual sensor updates, with freshness available | Last stored value shown for hours |
| Can setpoints be written reliably? | Official supported integration and bounded range | Undocumented reverse-engineered control with silent failure |
| Does the controller expose real pump state? | Separately documented output feedback | HA mirrors a command, not physical operation |
| What happens after a reboot? | Predictable room and source state | Stale automation leaves a zone in unintended mode |
| Is a manual room override respected? | Local wall control has priority | Automation immediately overwrites occupant decision |
| Is changing heating/cooling mode authorised? | Condensation and appliance control remain in charge | Generic relay can enable unprotected cooling |
Don’t let multiple controllers fight
A common poor result is a manufacturer thermostat managing schedules, Home Assistant applying another schedule, a smart TRV applying a third, and a boiler controller following its own weather compensation. Every few minutes, one system changes the other’s setpoint. Pick a clear master for time schedules and use other devices for supervision or compatible overrides. For heat pumps, weather compensation and compressor control generally remain with the manufacturer. Define what happens to a manual override and who restores the normal plan at the next scheduled boundary.
Worked project: eight rooms, twelve wet-floor loops
Take the earlier example: eight room control zones and twelve UFH loops. Assume seven rooms have one or two loops and one large open-plan zone has three. There is a 230 V or 24 V controller option under consideration; no hardware has yet been purchased. Before spending money, make these design decisions in a controlled sequence.
Step 1 — hydraulic schedule. A qualified designer calculates room heat losses, pipe spacing, loop lengths, design supply/return temperatures, manifold flow settings and pump head. The appliance’s minimum-flow and hydraulic-volume requirements are recorded, including all-closed valve conditions and defrost if applicable. Any buffer, bypass or separation arrangement is selected on that basis.
Step 2 — actuator schedule. Record all twelve valve bodies and the intended actuator family; confirm closing behaviour, mechanical interface, control voltage and steady/inrush consumption. If the designer uses four actuators in one room due to a revised pipe layout, re-check that one output can actually drive four heads.
Step 3 — controller capacity. An eight-zone controller may suit eight independent room demands, provided it has enough actuator outputs/terminals and documented aggregate current headroom. A controller advertised as “15 channels” may be overkill or appropriate depending on wiring practicality, sensor ecosystem and cooling functions. The maximum channel count is only one filter.
Step 4 — heat source. Specify what makes the source start, whether pump delay exists, what happens at zero open valves, which source is the master and how domestic hot water is prioritised. Verify dry contact versus bus interface; never derive the control wiring from a generic schematic for a different heat-pump model.
Step 5 — control and monitoring. Specify eight room temperature locations, optional floor-protection probes, appropriate manual controls, Home Assistant visibility and fallback behaviour. Pair all thermostats and explicitly test internet-down operation before occupancy.
Step 6 — commissioning. Map a warm-demand test one room at a time; observe the corresponding actuator power, eventual water flow and room-temperature response. Confirm the source and pump operate properly with small and large active loads. Record final manifold flows, photographs and labelled terminals in an as-built pack.
Why buying the cheapest separate components can cost more
Consider two illustrative, non-quoted budgets. Option A buys twelve low-cost actuators for £14 each, eight basic room controllers for £32 each, a £105 wiring centre and £180 of miscellaneous gateway/interfaces: hardware totals £709 before labour (12×£14 + 8×£32 + £105 + £180). Option B uses twelve compatible actuators at £25, eight thermostats at £45 and a £280 controller, with no external gateway required: £940 (12×£25 + 8×£45 + £280). Option B is £231 more on these hypothetical hardware line items. If Option A then needs several hours of additional wiring, one missed safety component or replacement of incompatible heads, its apparent advantage disappears. Conversely, a costly ecosystem does not prove better value where existing matched parts already work. These are arithmetic teaching examples, not current retail price claims or installation quotations.
A five-year cost comparison must also include commissioning, replacement batteries, any subscription, potential gateway replacement, documentation and future support. Claims of fixed energy savings percentages are not defensible without the house’s heat-loss and occupancy baseline. For a broader comparison of running and owning smart heating controls, see the planned article Smart Heating Total Cost: Thermostats, TRVs, Gateways and Energy Monitoring.
Commissioning checklist: prove the hydraulic outcome, not just an LED
Commissioning should start with insulation, electrical protective measures, manifold fill/purge, system pressure, water quality and pump settings as specified. Test one room at a time and allow the actuator’s specified transition time. Verify supply/return behaviour and actual manifold flow rather than merely hearing a relay click. Save the finished wiring, sensor and manifold schedules in a place future installers can find.
| Commissioning test | Expected evidence | What a failure may indicate |
|---|---|---|
| Loop identification | Correct room heats when corresponding demand is raised | Actuator/thermostat mapping error |
| Manifold flow setting | Loop reaches design flow with agreed test configuration | Air, closed head, wrong balancing or pump issue |
| Lowest-load operating case | Heat source operates within permitted hydraulic conditions | Insufficient flow/volume or improper bypass design |
| All-zone-demand case | Supply temperatures, pump flow and protection remain within spec | Under-sized plant, incorrect manifold balancing |
| Boiler pump overrun | Pump follows approved source logic after demand removal | Relay sequence incompatible with boiler |
| Heat-pump defrost/low-flow logic | Factory protections and min flow preserved | Bad hydraulic separation or excessive valve closure |
| Power loss to controller | Safe, documented head/source response | Unintended NO/NC or relay behaviour |
| Internet outage | Local thermostats remain functional | Critical cloud dependency |
| Cooling / humidity risk | Dew-point and floor-limit provisions operate | Unsafe cooling configuration |
| Manual room override | Occupants can request allowed setpoints | Competing automations or badly designed priority |
| Document pack | Loop labels, diagrams and part numbers recorded | High maintenance cost and future wiring errors |
Installation and maintenance mistakes to avoid
Do not mount manifold actuators where dripping water can enter their housings, or place electrical control boxes beneath an unprotected leak path. Do not bond a sensor directly against a pump motor body and assume it measures water temperature. Do not use adhesive tape as an electrical terminal solution. Do not conceal service valves behind permanent furniture. Do not replace a thermal actuator with a visually similar head unless voltage, mounting and stroke are all correct. And do not alter a heat pump’s flow switch or a boiler’s over-temperature protection because the new zoning system exposes an inconvenient lockout: the lockout is evidence to investigate, not a feature to suppress.
Troubleshooting guide: symptoms, causes and the next sensible test
| Symptom | Common possibilities | First safe check |
|---|---|---|
| Wrong room heats | Room-to-channel wiring or manifold label wrong | Compare as-built map with one-at-a-time demand logging |
| Zone LED on but floor cold | Thermal head opening slowly, no water flow, trapped air | Allow rated time; inspect approved flow indication |
| All rooms heat with thermostats off | NO/NC mismatch, valve stuck open, source control error | Record unpowered head state and controller command |
| Thermostats show demand but boiler never fires | Wrong heat-source relay wiring, boiler lockout, no approved demand | Check documented diagnostic/state screens; call installer |
| Pump runs constantly | Incorrect pump output selection, bypass/overrun strategy | Compare wiring centre outputs with manufacturer schematic |
| Boiler cycles rapidly | Small active load, poor flow, minimum power mismatch | Trend burner state, water temperature and active zones |
| Heat pump throws flow alarms | Too many closed heads, wrong pump/bypass design, air | Installer to verify min flow and protected operating cases |
| Floor overheats | Too-high supply temperature or missing floor limit | Stop unapproved control changes; professional inspection |
| Floor never reaches target | Heat-loss/design mismatch, low flow, sensor location | Compare design temperature and manifold flow schedule |
| Wireless thermostat drops offline | Battery, RF range, pairing or interference | Review local controller fault indications and logs |
| Home Assistant app shows stale values | Gateway, Wi-Fi, cloud latency, entity unavailable | Compare room stat screen to HA timestamp |
| Cooling causes surface moisture | Dew point not properly protected | Disable unapproved cooling and seek specialist inspection |
Frequently asked questions
1. Do I need one heating thermostat per underfloor heating loop?
No. One control zone may contain several manifold loops. The number of independently controlled room zones determines thermostat channels; the number of physical loops determines manifold connections and often the number of thermal actuators. The controller must support both the independent zone count and aggregate actuator load.
2. Is a twelve-port manifold the same thing as a twelve-zone controller?
No. It is a twelve-loop hydraulic distributor. Several loops can belong to one zone. A controller advertised as having twelve channels may still have specific limits on actuators per channel and total loading.
3. Can I mix 24 V and 230 V actuators on the same controller?
Not unless the controller has separately documented, electrically isolated output types that explicitly support both. Most wiring centres are intended for a defined actuator supply voltage. Never rely on adapter plugs or matching connector shapes to assume compatibility.
4. Should I buy normally open or normally closed actuator heads?
Choose the type specified by the controller and hydraulic safety design. NC heads generally close without power; NO heads generally open. Neither alone guarantees heat-source safety, minimum water flow or comfort when the controller fails.
5. How many actuators can I connect to one zone output?
Only the number permitted by that exact controller and actuator combination. Check per-output power/current, start-up characteristics and total board capacity. Headcount alone can be misleading when different actuators draw different power.
6. Will any Zigbee thermostat pair directly with a Zigbee wiring centre?
No. Zigbee radio support does not ensure compatible device clusters, commissioning keys or manufacturer integration. Proprietary systems may use Zigbee transport but still require their own coordinator. Verify tested interoperability for the exact models.
7. Can Home Assistant operate the manifold directly through eight smart relays?
Technically a controller can request individual outputs through suitable interfaces, but that is not a good default design for permanent heating. You would need to engineer electrical isolation, interlocks, delays, manual fallback, circulation and appliance-safe control. Use a purpose-built heating controller and integrate at its supported interface where possible.
8. Will a heat pump be more efficient with every room independently zoned?
Not necessarily. Excessive closing of loops can reduce flow and runtime stability and interfere with minimum volume or defrost. Low-temperature distribution, weather compensation, envelope quality and hydraulic design may matter more than numerous on/off zones.
9. Does every wet underfloor heating system require a mixing valve?
No. A direct low-temperature heat-pump UFH design may not. A mixed-temperature boiler and radiator arrangement often needs more hydraulic control. Use the designer’s supply-temperature limits and the appliance/manifold instructions; do not fit a mixing group solely because a generic kit advertises one.
10. What happens when all room thermostats are satisfied?
The controller should stop room heat demands and actuators move toward their unpowered state as designed, but pumps, appliance overrun and minimum-flow protection follow the engineered system logic. The correct behaviour varies with source and hydraulic topology and must be verified in commissioning.
11. Do I need a buffer tank for a zoned heat pump?
It depends on the manufacturer’s minimum-flow and water-volume requirements and the hydraulic arrangement. A buffer can sometimes be appropriate but adds losses and mixing opportunities. It is not a universal cure and should be sized and positioned by the designer.
12. Can smart thermostats replace floor temperature sensors?
A wall thermostat primarily measures air temperature. A floor-limit probe may be needed to protect floor finishes, constrain surface temperature or enable safe cooling. Home Assistant’s room-temperature value is not an independent physical floor-limit control.
13. How fast should a thermal actuator open?
Typically over minutes, but the exact timing is manufacturer- and temperature-dependent. A relay switching on is not proof that water flow appears instantly. Allow the rated travel time and confirm via relevant manifold diagnostics.
14. Is 24 V always safer or better than 230 V?
It can offer a suitably designed low-voltage actuator arrangement, but electrical safety depends on the complete system and its isolation, transformer and installation. Reliability and suitability come from certified, correctly matched hardware rather than voltage alone.
15. Can an OpenTherm boiler be enabled with the wiring centre’s dry contact?
Only if the boiler also has an approved on/off demand input and the manufacturer specifies that control method. OpenTherm’s digital thermostat terminals should not be treated as generic relay terminals. Using a dry contact can also surrender modulation benefits of a compatible digital controller.
16. Should I use a valve position signal or a thermostat call as proof of actual water flow?
Neither is definitive. Thermostat demand is a request; actuator position may be a command; and a valve can remain obstructed or unbalanced. A properly located flow sensor or meter provides stronger hydraulic evidence. Many installations rely on commissioning readings rather than permanent per-loop sensors.
17. Will my zone controller work if the internet goes down?
A well-designed local controller can continue operating with its own thermostats without a cloud connection, but this is model-specific. Test an internet outage before relying on the system and distinguish Wi-Fi local connectivity from external internet service.
18. What is the most useful Home Assistant dashboard for multi-zone heating?
Show per-room setpoint and temperature, controller heat demand, appliance operating state, flow and return temperature, available pump state, outdoor temperature and any alarm. Keep time histories and state freshness. Distinguish commanded status from verified physical measurements.
Final buying recommendations
If you already have a working installation, reuse its matched controller and actuators unless there is a documented incompatibility or safety issue. Add Home Assistant through supported telemetry before replacing wired controls. If building from scratch, have the designer specify hydraulic loops and heat-source requirements first, then choose a coherent controller family. Buy components by exact part number, output voltage and support matrix, not a search result’s “8 zones” label.
For 230 V ecosystems with conventional wiring, a documented Heatmiser UH-series configuration is a strong starting point where its terminals and room controls fit the design. For integrated 24 V floor control, Danfoss Icon2 or Uponor Smatrix deserve evaluation using their exact manufacturer model documents. SALUS has both 230 V and 24 V wiring-centre families—select the variant deliberately. For any system, confirm the pump and heat-source outputs, local failure behaviour, commissioning documentation and installer support before prioritising mobile-app appearance.
Finally, the controller must respect the physics of the heating system. Floors respond slowly; heat pumps need suitable flow and volume; boilers may dislike tiny instantaneous loads; and a smart relay does not replace protected hydraulic and electrical design. Monitor first, commission thoroughly and optimise only after the baseline system works.
Sources and technical references
- Heatmiser — Underfloor heating wiring centres: UH variants, zone output characteristics, actuator limits and supported arrangements.
- Heatmiser UH8 — installation manual: a reference for a specifically defined 230 V wiring-centre version; never substitute its wiring diagram for a different model.
- Danfoss Icon2 24 V main controller product specification: exact part-number output and actuator limitations.
- SALUS KL08RF24V UK product information: zone and actuator count for the named voltage-specific variant.
- Uponor Smatrix Base Pulse installer information: 24 V AC actuator compatibility, zones, channels and commissioning.
- Daikin heat-pump installer reference guide: example of manufacturer-specific minimum water-flow and bypass requirements; not a universal design template.
- Home Assistant — Generic Thermostat: software thermostat capabilities and control boundaries.
- Home Assistant — History Stats: duration measurement used in the monitoring-only example.
- ESPHome — Switch component: useful for supervised telemetry and defined boot behaviour, without replacing electrical safety measures.
- ESP32.co.uk — Multi-zone heating controller with ESPHome and Home Assistant: companion electronics guide.