Thermostatic radiator valve (TRV) not working correctly
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Most likely cause & what to check
If the radiator is always cold even on a high TRV setting: the pin inside the TRV body may be stuck down. Remove the TRV head (unscrew the cap nut) — you will see a small metal pin. Press it in and out with a finger — it should spring back up freely. If stuck, wiggle it or gently tap with a screwdriver handle.
Spray a small amount of WD-40 around the pin if it is stiff, then work it back and forth until free.
If the radiator is always hot regardless of the TRV setting: the pin is stuck up (open position) and the valve isn't closing. The same remedy applies — free the pin.
If the TRV body is the problem after freeing the pin, replace the TRV head — they are available for £10–25 and simply screw onto the existing valve body. Check the brand and connection size matches.
Set the TRV to your desired level (2–3 is typically 18–20°C) and leave for 30 minutes to see if the room temperature stabilises.
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Frequently asked questions
Can I replace just the TRV head without touching the pipework?
Yes — the head screws onto the valve body. As long as the body is compatible, you can swap the head without any plumbing work or draining the system.
What number should I set my TRV to?
The numbers are not degrees — they represent approximate heat output. Setting 3 is typically around 20°C in most UK homes. Experiment to find what suits each room.