TRV stuck closed — radiator not heating up
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Most likely cause & what to check
If a radiator is cold despite the heating being on, the TRV may be stuck in the closed position. This is very common after summer — the pin inside the valve corrodes slightly and gets stuck when the heating is restarted in autumn.
Remove the TRV head: it unscrews or lifts off (some have a locking ring). Underneath you'll see a small metal pin protruding from the valve body.
Try pressing the pin in and releasing it several times. If it moves freely (springy action), the valve mechanism is fine — the head may be the problem (fitted in the wrong position, or thermostat faulty).
If the pin is stuck down (compressed) and won't spring back up, it's seized in the closed position. Apply a few drops of WD-40 around the base of the pin and leave for 5 minutes. Then try pressing and releasing again.
If still stuck, grip the pin with pliers and gently pull it upward. It should pop free. If you cannot free it, the valve body may need replacing.
Refit the TRV head and set it to a mid-level temperature (position 3 or 4). The radiator should now heat up.
To prevent this happening again, fully open the TRV head at the end of each heating season and briefly run the heating in summer (once a month is enough) to keep the pin moving.
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