The DS18B20 is one of the most robust and accurate digital temperature sensors for:

• Boilers & hot water tanks
• Underfloor heating
• Outdoor monitoring
• Aquariums
• HVAC pipes
• Radiators
• Freezers

It uses a 1-Wire protocol, allowing multiple sensors on the same wire, making it perfect for home automation.

This guide includes two methods:

1. ESPHome (recommended — auto-discovery)
2. MQTT (manual)

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1. Parts Required

• ESP32 DevKit
• DS18B20 waterproof probe
• 4.7k resistor (required)
• Jumper wires
• USB cable

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2. DS18B20 Wiring Diagram

Required connections:

ESP32 → DS18B20
3.3V → VDD
GND  → GND
GPIO4 → DATA
4.7k resistor between DATA and 3.3V

METHOD 1 — ESPHome Integration

This is the easiest method for most users.

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3. ESPHome YAML for DS18B20 (Working Code)

esphome:
  name: esp32-ds18b20
  platform: ESP32
  board: esp32dev

wifi:
  ssid: "YOUR_WIFI"
  password: "YOUR_PASSWORD"

logger:
api:
ota:

# 1-Wire bus
dallas:
  - pin: 4

sensor:
  - platform: dallas
    address: 0x3c0000031aa7c828
    name: "Boiler Temperature"
    update_interval: 5s

Notes:

• If you don’t know the sensor’s address, omit address:
• ESPHome will auto-detect the sensor and show its ID in logs
• Then you can add the address for stability

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METHOD 2 — MQTT Integration (Matches Your Actual Setup)

If you use MQTT sensors inside Home Assistant’s mqtt: section, here is the correct YAML for your configuration style.

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4. Home Assistant configuration.yaml (Correct MQTT Code)

Add under:

mqtt:
  sensor:

Correct DS18B20 MQTT YAML Block

mqtt:
  sensor:
    - name: "Boiler Temperature"
      state_topic: "home/boiler/ds18b20"
      value_template: "{{ value_json.temperature }}"
      unit_of_measurement: "°C"

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5. ESP32 Arduino Code for DS18B20 (MQTT Publisher)

#include <WiFi.h>
#include <PubSubClient.h>
#include <OneWire.h>
#include <DallasTemperature.h>

#define ONE_WIRE_BUS 4
#define WIFI_SSID "YOUR_WIFI"
#define WIFI_PASS "YOUR_PASSWORD"
#define MQTT_SERVER "192.168.0.10"

WiFiClient espClient;
PubSubClient client(espClient);

OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);

void setup() {
  Serial.begin(115200);
  
  sensors.begin();

  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) delay(500);

  client.setServer(MQTT_SERVER, 1883);
}

void loop() {
  if (!client.connected()) {
    while (!client.connected()) client.connect("ESP32_DS18B20");
  }

  sensors.requestTemperatures();
  float tempC = sensors.getTempCByIndex(0);

  String payload = "{\"temperature\":" + String(tempC) + "}";

  client.publish("home/boiler/ds18b20", payload.c_str());

  client.loop();
  delay(5000);
}

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6. Adding Multiple DS18B20 Sensors

If you add more sensors, all can share the same DATA wire.

MQTT example:

mqtt:
  sensor:
    - name: "Tank Top Temperature"
      state_topic: "home/boiler/ds18b20/top"
      value_template: "{{ value_json.temperature }}"
      unit_of_measurement: "°C"

    - name: "Tank Bottom Temperature"
      state_topic: "home/boiler/ds18b20/bottom"
      value_template: "{{ value_json.temperature }}"
      unit_of_measurement: "°C"

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7. Home Assistant Dashboard Example

type: vertical-stack
cards:
  - type: sensor
    entity: sensor.boiler_temperature
  - type: history-graph
    hours_to_show: 24
    entities:
      - sensor.boiler_temperature

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8. Example Automation

Automatically switch boiler off when water reaches 55°C:

automation:
  - alias: "Boiler Auto Shutoff"
    trigger:
      - platform: numeric_state
        entity_id: sensor.boiler_temperature
        above: 55
    action:
      - service: switch.turn_off
        target:
          entity_id: switch.boiler_relay

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9. Troubleshooting

Sensor reads -127°C

• Missing 4.7k pull-up resistor
• Broken cable
• Wrong data pin

Sensor shows 85°C

• DS18B20 not initialized
• First reading after boot (normal)

Sensor drops randomly

• Long cable → use shielded cable
• Add 100nF capacitor between VDD/GND

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10. Why DS18B20 Is Perfect for Boilers & Heating

Feature	Benefit
Waterproof probe	Can be attached to pipes/tanks
Long cables OK	Up to 20–30 meters with shielded cable
Very stable	Does not drift over time
Multiple sensors per wire	Boiler top/bottom / pipes

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