Boiler doesn’t turn off (sometimes)

[Foss13]

I have an IKON-T combi boiler that operated radiators with TRVs (via the boiler timer) and hot water until about five years ago when I had a new kitchen fitted with under floor heating. This was added to the existing system and ran from a JG Aura thermostat.
A couple of years ago we had occasional problems with the boiler continuing to run (obvious in the middle of the night). Switching on and off via settings on the thermostat saw it running properly again on the programme. The same thing happened occasionally last winter. Yet again this year I am finding the same thing but I have had to do a lot more toggling on and off to get it to finally switch off on several occasions already. Obviously I also have the possibility of just switching the boiler to the ‘summer’ setting but I would prefer it to be working properly.
I am thinking of asking the service engineer to look at it at the next service, but obviously intermittent faults can be problematic…
It seems strange to me that the boiler will always switch on when commanded by the thermostat but sometimes struggles to switch off and then obviously needs quite a jog (switching on and off repeatedly) to do this.
Any ideas what is going on, so I can be clear to the service engineer (tell him to bring the right part etc.)?

 

[Gasguru]

I'd consider getting a simple light switch wired in series with the wire to control the boiler heating ....that will enable you to tell whether it's actually a boiler problem or external controls that are failing to turn off.

 

[stem]

I had a new kitchen fitted with under floor heating. This was added to the existing system and ran from a JG Aura thermostat.

If the kitchen has a separate thermostat which allows control separately from the rest of the house, the kitchen will have its own dedicated heating zone. In which case it will have its own motorised valve controlling it. If so, the thermostat is only responsible for opening and closing the motorised valve. In turn, the motorised valve has a microswitch inside that starts the boiler when the valve is in the open position. These microswitches can stick and cause the boiler to run even if after valve is closed. Switching the thermostat on and off and causing the valve to move from open to closed can sometimes release it.

If your system has this configuration and you know where the motorised valve is, you can check to see if the thermostat is opening and closing the valve as it should.

 

[CBW]

If there is a link inside the boiler or on the underfloor heating system, that could be keeping it on?

 

[Foss13]

If the kitchen has a separate thermostat which allows control separately from the rest of the house, the kitchen will have its own dedicated heating zone. In which case it will have its own motorised valve controlling it. If so, the thermostat is only responsible for opening and closing the motorised valve. In turn, the motorised valve has a microswitch inside that starts the boiler when the valve is in the open position. These microswitches can stick and cause the boiler to run even if after valve is closed. Switching the thermostat on and off and causing the valve to move from open to closed can sometimes release it.

If your system has this configuration and you know where the motorised valve is, you can check to see if the thermostat is opening and closing the valve as it should.

Thanks, that sounds like it might be a possibility. Having a look at all the obviously new work around the boiler there is a blue cube about 3in. Square with a small metal lever on the side which moves when the boiler switches on, whether it is via the timer for the old CH system, hot water or the new UFH system. Strangely it doesn’t seem obviously electrically connected to the boiler itself but it is certainly a motorised valve. It sounds like this should be the starting point when I call an engineer out.

 

[stem]

If it's something like this:

Then the thermostat will open / close the valve and the grey and orange wires from the motorised valve are what control the boiler.