My TRV’s all seem to be stuck on full, I have no control just red hot or off. Looked up a couple of guides about unsticking pin once the head is off but mine doesn’t look the same, It looks similar to this (If that pic works) is the top bit still the pin?
Could be stuck in the off (down) position. Drain rads. and try removing the brass fitting to see if can free the pin. If yes grease it with plumbers grease and re-fit it IF you wish to chance it. Try with the thermostat cap in place. If seems Ok you can chance it and fill rads. Don't forget the inhibitor. You could flush rads. if need to do so. I would be inclined to fit a new valve for peace of mind as not expensive.
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