Should the radiator in the same room as the thermostat have a TRV?

A room thermostat measures one room and controls the whole boiler. A TRV measures one room and controls one radiator. Put both in the same room and you have two devices trying to control the same temperature with completely different consequences.

Step by step

1. Find where the room thermostat is.Usually a hallway, a landing or a living room. That room is the reference for the entire heating system.
2. Check what valve is on that room's radiator.A thermostatic head with numbers means a TRV. A plain cap on both ends means it has none, which is what you want.
3. Understand the conflict.If the TRV shuts that radiator, the room cools, and the thermostat keeps calling for heat. The boiler runs, every other room overheats, and the reference room never satisfies.
4. Set it fully open if a TRV is fitted.The simplest fix. Turn it to maximum and leave it there permanently, so the room thermostat is the only control acting on that room.
5. Consider removing the head altogether.Replacing the thermostatic head with a plain cap or a manual head removes the temptation to adjust it and makes the intent obvious to anyone else in the house.
6. Check the thermostat is not next to a heat source.Above a radiator, in direct sun or beside a lamp, it satisfies early and the whole house is cold. That is a separate and equally common fault.
7. Keep at least one radiator without a TRV.Most systems need a path for the water when everything else has closed. The thermostat room's radiator conventionally serves that purpose.
8. Reconsider if you have smart valves.A full smart TRV system with a compatible controller manages this by coordinating the valves with the boiler demand. In that case the usual rule does not apply — follow the system's instructions.
9. Check the results over a few days.Every other room should now reach temperature at a similar time to the thermostat room, and the boiler should cycle less.

Tips

• If you take the head off, fit a plain cap so the valve stays clean and nobody tries to adjust it.
• The thermostat room is the room that decides for the whole house. Where it sits matters more than any TRV setting.
• Never fit a TRV to a radiator in a room where you also want the boiler to be controlled from — the two cannot both win.

Common mistakes

• Turning down the TRV in the hall to save money — The hall thermostat then never satisfies and the boiler runs continuously, heating every other room. It costs more, not less.
• Putting a TRV on every single radiator — If they all close, the pump is running against a closed system. Most installations need at least one radiator or a bypass permanently open.

If it doesn't work

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