mbirth 🇬🇧

Collector of social media accounts. Speaks 🇬🇧 and 🇩🇪.

  • 2 Posts
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Joined 2 years ago
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Cake day: June 1st, 2023

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  • The Junkers boiler at my previous place had an emergency mode where it was heating when the contacts were open. Even their simplest thermostats put a load on the wires depending on how much heat is required - so it doesn’t go full blast when you are only slightly under the target temperature.

    So, this all depends on your specific boiler. While it might work with a simple relay, it might be far from optimal in terms of energy efficiency and wear&tear of the boiler.



  • Despite the name it’s not a simple on/off that can be done with a relay. Those 2 wires also provide power to the thermostat unit. I’d first try to find more information about how these thermostats report demand to the boiler before using a relay.

    I’ve also seen someone that simply replaced the NTC/PTC on their existing thermostat with some ESP circuit so they basically controlled what the thermostat “sees”. Want more heat? Tell the thermostat that it’s 5℃ in the room. Want the boiler to stop? Simulate a cozy 30℃.


  • That’s a Honeywell T87G1006 “On/Off” thermostat. “On/Off” meaning that it can signal to the boiler whether more heat is needed or not. Boilers of that time may also be compatible with the OpenTherm protocol as there’s a similar model that also speaks OpenTherm.

    The easiest way to go about this is probably to look for a more modern thermostat that’s compatible with your boiler but also provides some interface for remote control from your Home Assistant.