OpenTherm Gateway

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OpenTherm Gateway
Opentherm spacegateway.jpg
Owner The_Niz
Status Infra
Location Kitchen wall
Tool Yes
Tool category General

OpenTherm Gateway


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Kitchen wall


OpenTherm gateway has been put between the heater and the thermostat. This way we are able to read the OpenTherm communication between them, and control the heater using the gateway. It is a board with a PIC controller that already came pre-flashed. It can be used with a FTDI cable or you can put an ESP8266 based NodeMCU board on it and communicate with that over Wifi. We first went for the ESP8266. The ESP8266 ran Espeasy with Ser2Net. We later changed it with USR-TCP232-T2.


Boiler: Remeha Calenta (

Integration with home assistant

We do not use py-otgw-mqtt on Jarvis anymore but are using native OpenTherm support in Home Assistant.

  • IP:
  • Port: 20108

For the CH return water temperature to be reported successfully the serial command AA=28 has been issued ( This command should persist in the OTGW and only be needed once. If however the return water temperature is once again missing and the Calenta is still used the command may be issued again.


  • Update Remeha iSense thermostat firmware if possible
  • Get notified when water pressure is low


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