Fitzy71:
I’m not sure if it’s S or Y plan to be honest. It’s a combination boiler with the big expansion cylinder above the hot water tank.
Are you sure it is a combi? Sounds like you have an un-vented cylinder for the hot water. Anyway, which model is your existing honeywell room thermostat? We should be able to find the wiring diagram for it somewhere
Fitzy71:
I’m not sure if it’s S or Y plan to be honest. It’s a combination boiler with the big expansion cylinder above the hot water tank.
Are you sure it is a combi? Sounds like you have an un-vented cylinder for the hot water. Anyway, which model is your existing honeywell room thermostat? We should be able to find the wiring diagram for it somewhere
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