MQTT interface for De Dietrich boilers with Diematic 3 / 4 / Delta regulator

Control and monitor your De Dietrich boiler through MQTT using a Raspberry Pi (or any Linux host running Home Assistant OS).

This is a fork of Benoit3/Diematic_to_MQTT with two major additions:

1. USB RS485 serial transport – connect a cheap USB RS485 dongle directly to your HA host without a network adapter.
2. Home Assistant OS native add-on – install and configure everything from the HA UI without touching the command line.

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Hardware

The Diematic 3 regulator exposes a Modbus RTU RS485 port (Mini-DIN 4).

Adapter	Config
USB RS485 dongle (CH340, FTDI, …)	connectionType: serial
RS485-to-Ethernet/Wi-Fi (USR-TCP232-306, …)	connectionType: tcp

USB RS485 dongle example:

Wiring (Mini-DIN 4)

Pin 1 (D+)  → RS485 A+
Pin 2 (D-)  → RS485 B-
Pin 3 (GND) → GND  (optional but recommended)

Modbus parameters

Parameter	Value
Mode	RTU (binary)
Baud rate	9600
Frame	8N1
Boiler address	0x0A (10 decimal)

Dual-master timing – The Diematic 3 alternates between acting as Modbus master (5 s) and slave (5 s). Response times are therefore 5–10 s; keep period ≥ 10 s.

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Installation

Option A – Home Assistant OS Add-on (recommended)

1. In Home Assistant go to Settings → Add-ons → Add-on store → ⋮ → Repositories.
2. Add the URL of this repository.
3. Install Diematic to MQTT from the list.
4. Fill in the options (see ha-addon/DOCS.md or the HA UI info tab) and click Start.

The add-on generates its own configuration file from the HA options and runs the Python bridge in an isolated container. Serial (/dev/ttyUSB*) and UART devices are automatically exposed to the container via the uart: true flag.

Option B – Docker (standalone)

docker run -d \
  --device /dev/ttyUSB1 \
  -v $(pwd)/src/conf:/app/conf \
  ghcr.io/ababilone/diematic_to_mqtt:latest

Edit src/conf/Diematic32MQTT.conf before starting (see configuration below).

Option C – Python directly (Raspberry Pi / Raspbian)

pip3 install -r src/requirements.txt
cd src
python3 Diematic32MQTT.py

See the Wiki for the systemd service setup.

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Configuration (Diematic32MQTT.conf)

[Modbus]
# connectionType: serial  → USB RS485 adapter
# connectionType: tcp     → RS485-to-Ethernet adapter (original)
connectionType: serial

# Serial mode
serialPort: /dev/ttyUSB1
baudrate: 9600

# TCP mode (used when connectionType = tcp)
ip: 192.168.1.X
port: 20108

regulatorAddress: 0x0A
interfaceAddress: 0x32

[MQTT]
brokerHost: localhost
brokerPort: 1883
brokerLogin:
brokerPassword:
topicPrefix: home/heater
clientId: boiler

[Boiler]
regulatorType: Diematic3   # Diematic3 | Diematic4 | DiematicDelta
timezone: Europe/Paris
timeSync: False
period: 10
enable_circuit_A: False
enable_circuit_B: False

[Home Assistant]
MQTT_DiscoveryEnable: 1
discovery_prefix: homeassistant

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Home Assistant Integration

MQTT discovery is enabled by default. Once the bridge is running, the following entities appear automatically:

Sensors – boiler temperature, return temperature, exhaust temperature, external temperature, zone A/B ambient temperature, ECS temperature, water pressure, burner power, fan speed, ionisation current, pump power, alarm.

Binary sensors – burner status, zone A/B pump, hot-water pump.

Selects (control) – zone A mode, zone B mode, hot-water mode.

Numbers (control) – day/night/antifreeze setpoints for zone A, zone B, and hot water.

Switch – sync boiler clock to HA time.

Make sure your MQTT integration birth-message topic is homeassistant/status with payload online for discovery to work after a restart.

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Known limitations

• Remote display heating mode not updatable without a workaround.
• No support for switching between programs (P1–P4).
• ECS pump info not fully reliable.
• Permanent antifreeze mode replaces temporary antifreeze (hardware limitation).
• Pump power stays at 100 % when all pumps are off.

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References

• Original project: Benoit3/Diematic_to_MQTT
• Home Assistant Community thread
• Fibaro forum (French)