Vaillant boiler overheating (F20)

starconf

Sorry, I missed that the TRV in that room was not a Tado.

With your setup whichever room Thermostat 3 is in(Attic?) should be set to never heat in the Tado App, have it permanently off. If Thermostat 3 is set to heat that room but the non Tado TRV is closed then there will be nowhere for the water to flow.

Titerito

What if the Thermostat 3 is always open, as well as the non Tado TRV? If the thermostat 3 is always off, how do the Tado smart valves communicate with the boiler ?

starconf

You could do it that way and set the non Tado TRV to fully open, but the problem is that radiator will still have water flowing when any other room calls for heat and so the attic room will get very hot.

Even with Thermostat 3 set to off in the app, it can still command the boiler to turn on if it is the zone controller for other rooms. You could set Thermostat 3 to a schedule where it is permanently off and then whenever a different room requests heat it will relay the command to Thermostat 3 and that will then turn on the boiler (as long as Thermostat 3 is set as the zone controller for that room). Thermostat 3 in this case is acting purely as a relay and not as a Thermostat itself, but there is no real problem with that.