TRV Not Working? How to Diagnose and Fix a Faulty TRV
If a radiator is stuck permanently hot, permanently cold, or ignoring the TRV setting, the valve is a likely culprit. The good news is that the most common TRV fault takes minutes to fix.
The most common fault — a stuck pin
Under every TRV head is a spring-loaded pin. Over the warmer months, if the valve has sat closed, the pin can stick down and hold the radiator shut — so the radiator stays cold even with the head turned up. Unscrew the head and gently tap or wiggle the pin (a pair of pliers helps); it should spring freely up and down. Free it, refit the head, and the radiator should work again.
Radiator stuck hot
If a radiator is always hot regardless of the TRV setting, the pin may be stuck up (open), the head's internal sensor may have failed, or the head may not be seated correctly on the valve. Try removing and refitting the head fully; if it still won't control, the head or valve needs replacing.
Radiator won't get hot
First rule out the simple things: is the head turned up, is the lockshield at the other end open, and is the rest of the system heating? If other radiators are fine but this one stays cold, it's usually a stuck pin (see above) or trapped air — bleed the radiator to check.
Check the setting and location
TRV numbers are target temperatures, not on/off — setting 3 suits most rooms. Also make sure the head isn't blocked by curtains, a radiator cover or furniture, and isn't in the same room as your main thermostat, or it can't sense the room properly.
When to replace the TRV
If freeing the pin and refitting the head doesn't restore control, the head or the whole valve has failed. A genuine Myson TRV2 replacement restores accurate, A-rated control. See our guide on how to replace a TRV.
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