Boiler sending heat, nothing asking for it.

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Looking for some help or maybe a common sense suggestion.

We have a Baxi Assure Combi Boiler, with 2 Honeywell T3 thermostats (one upstairs controlling those radiators, one downstairs controlling those).

Had an issue today where the boiler came on without either thermostat asking for heating, but the boiler showing as sending hot water out to the radiators. Both thermostats were set at 19C, with the house temp on both showing as 22C. Only the upstairs radiators were getting hot, and after a little bit upstairs was sitting at 26C with the boiler still sending heating up but the thermostat not asking for anything.

I’ve tried resetting the thermostat, resetting the boiler etc, but every time I switch it back on it just kicks in and starts sending heating to the upstairs zone.

Has anyone had anything similar, or have any common sense suggestions for what the issue could be?

For reference, the house is a new-build, 2.5 years old, thermostats and boiler all the same age, and boiler serviced each year.

Thanks!
 
Possibly a stuck or failed 2 way / 3 way port. I don't have a combi but most systems have a port that opens to send hot water to the rads when they call for it but closes when you only need hot water for your taps etc. The motor that drives the valves can get stuck or just fail - I had to fit a new one last year and it's a fairly straightforward job.
 
Possibly a stuck or failed 2 way / 3 way port. I don't have a combi but most systems have a port that opens to send hot water to the rads when they call for it but closes when you only need hot water for your taps etc. The motor that drives the valves can get stuck or just fail - I had to fit a new one last year and it's a fairly straightforward job.
Ah I see, could possibly be that, thanks!
 
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