Thermostat Problem

[Avo Mk8]

Thank you for your reply.

We have always thought the flame symbol showed the thermostat was communicating with the boiler. The fact that we have not seen it at all since this started was very confusing.

'So in normal operation, when the temperature is at 13 degrees first thing in the morning and you up the target temperature to say 20 degrees then you should see a radio signal briefly flash up and then the flame symbol should remain on. When 20 degrees is reached, the flame symbol will go off (and the green light on the relay box should go off as well).' That is exactly what happened before but as described above we are seeing no flame symbol now.

To be honest I have not noticed if the green light was always on before but if pressed I would say it wasn't on all the time.

So to summarise:
The green light on the BDR91 is on all the time. That is not normal behaviour.
The green light (which indicates demand for CH) should only come on when the thermostat demands heat (showing the flame symbol) and should otherwise be off.

My understanding is that there should be two way communication between BDR91 and DT92, ie that both receive and transmit, when one transmits an instruction the other acknowledges it.

So one hypothesis is that the BDR91 is 'stuck' with the light on. And is not acknowledging a command, so the DT92 is showing a communication failure. You might try power cycling the BDR91 (turning off, wait a minute, turn on).
If that doesn't do anything, changing the BDR91module would prove if that's faulty. But that is stooping to the 'swapping parts' method of fault finding, which I don't encourage.

All I can suggest is:
Power cycle the BDR91. See if you can get the green light to turn off, and if you succeed, check that the CH stops accordingly.
Take the DT92 up to the BDR91 location and see if you can get the two of them talking to each other, by pairing or factory reset etc.
If that proves impossible, replace the BDR91 module.
If that doesn't fix it, replace both the BDR and DT pair with another solution!

All this assumes the boiler is not at fault in any way!

 

[Alk]

I agree with Avo Mk8 that it seems that the relay box has got stuck and the 2 way communication is no longer working. I was also going to suggest to power cycle both the thermostat (remove the batteries for at least 15+ minutes) and relay box.
However, my concern with power cycling the relay box is that you have a system boiler/gravity hot water setup and so you may have an old boiler with a pilot? Do you have an old boiler with a pilot or a modern boiler without a pilot?
In order to cut power to the relay box, you are also switching power off to the boiler and if you have an old boiler with a pilot, then you have to re-light the boiler pilot and there is a risk with this that you then don't have heating if the boiler won't re-light. However, if you have a modern boiler that does not have a pilot, then you don't have this risk and turning the power off to the boiler and relay box is less risky. I hope that makes sense?

Depending on the outcome of how you proceed and how things pan out, I would also suggest that you reach out to Honeywell (now renamed Resideo) support on 03001301299 (freephone number). Also have a look over the installation manual for your thermostat which you can have in front of you at the same time to know what Honeywell might direct you to do: Honeywell DT92E Wireless Room Thermostat Installation Manual - thermostat.guide - https://thermostat.guide/honeywell/honeywell-dt92e-wireless-room-thermostat-installation-manual/ (this is the "advanced" guide for installers - not the consumer guide!).

Finally, again, depending on the outcome of what you find and/or what Honeywell support help you to troubleshoot as to the exact fault, should you need a tradesmen to replace parts, I would recommend that you reach out to your local Age UK branch who should be able to put you in touch with a relevant tradesmen at discounted rates. Be it an electrician, heating engineer or even a multiskilled handyman that is proficient in basic plumbing and electrics.

Bear in mind that the relay box and thermostat are paired together at the factory. So should you replace individual components they will need to be rebound, which you have already explained is inaccessible for you to do.