UK Boiler control and Thermostat | Home Assistant | Page 1

sonic hedge Sep 15, 2025, 10:52 AM

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Hi everyone,

I am interested in getting some exposure to my boiler functionality, so turn on heating, turn off, current temp of the room in which the thermostat is present etc.
It would be GREAT to get a solution that doesnt involve a cloud or 3rd party for it to function.

Thermostat also needs to be wireless so I can move it around.

I am very new to HA so I don't really know what I am doing in terms of the various open protocols available etc, but it would be good to understand what my options are.
Using google hasnt really given me much to go on yet.

Thanks in advance everyone.

void cobalt Sep 15, 2025, 12:49 PM

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What boiler do you have?

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Do it have smart inputs?

sonic hedge Sep 15, 2025, 1:02 PM

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its a Baxi combi boiler.
There is nothing smart on it at all.
But it does currently have a wireless thermostat. I can take a pic of it, if it would help.
I can also get the model # of the boiler too if that helps

void cobalt Sep 15, 2025, 1:13 PM

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Model number may help

sonic hedge Sep 15, 2025, 1:19 PM

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Baxi Avanta 39c exclusive.
This is my current termostat - pic attached

WhatsApp_Image_2025-09-15_at_14.17.09.jpeg

void cobalt Sep 15, 2025, 2:08 PM

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Hmmm, honestly i dont know. I cant figure out if it supports opentherm.

sonic hedge Sep 15, 2025, 3:18 PM

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You mean the boiler?

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According to google it does not

The Baxi Avanta 39C is not an OpenTherm boiler by default, as it was manufactured by Remeha and uses a simpler single-channel control system, not the more advanced OpenTherm protocol. While Baxi boilers in general can work with OpenTherm, this specific model lacks the inherent capability; you would need a separate OpenTherm gateway to achieve communication with the boiler.

So where does that leave me? any options outside of buying a full new boiler? 😄

marble valley Sep 15, 2025, 4:10 PM

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A Shelly smart relay can be used to control the 'call for heat' signal of the boiler remotely. That can be connected to Home Assistant or other Shelly products like the wall display / thermostat

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it's not exactly plug & play, but it's simpler and cheaper than a new boiler

sonic hedge Sep 15, 2025, 5:40 PM

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Is there any kinda guides or something that might take me through it?

marble valley Sep 15, 2025, 6:11 PM

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what I did was to find the wiring diagram for my (Baxi) boiler and connect the thermostat terminals (bk1 and bk2) to the relay terminals (left side). The relay also needs power, which may be simple depending on how the current thermostat is wired in.

I was able to hook all this up myself, but I'd recommend getting a professional involved if you're not confident with electrics

#UK Boiler control and Thermostat