For anyone looking to tinker with automating their thermostat, I highly recommend looking at the OpenTherm Gateway[1] (OTGW). It uses the OpenTherm protocol whi

For anyone looking to tinker with automating their thermostat, I highly recommend looking at the OpenTherm Gateway[1] (OTGW). It uses the OpenTherm protocol which is supported by a lot of heating systems. Though the protocol is backwards compatible with the old type of thermostat which would simply turn on and off for heating, OpenTherm works with modulation as well. Not simply turning the heating on at 100% capacity and turning it off again when the target temperature was reached, but taking a bit more of a gradual approach. The OTGW fits in here beautifully. It sits in the middle between your heating system and your existing (OpenTherm-speaking) thermostat. Listening to all the messages being sent between your heating system and thermostat. And if the onboard firmware fails, it should even fall back to that behavior completely. For me, it allows to get a ton of information from my thermostat and heater, and automate heating and cooling down my home. All in a much better way than a simple relay with an ESP8266/ESP32 could do. It also retains my (non-smart) home thermostat functionality, including the ability to change setpoints on it. Which is much appreciated by my partner. Third party support for the OTGW is relatively good as well. Home Assistant and Domoticz both support the OTGW, and the serial protocol it speaks is quite simple as well. Best of all, its opensource and has no need for any cloud connection you don't want. [1]: https://otgw.tclcode.com/ https://otgw.tclcode.com/