My elderly neighbour rang me this morning to say her radiator was not working whan she opened the door the heat hit me she has TRV rads I tried to explain that when the temperature falls they will open and will keep the room to the temperature she wants I demonstrated this by opening the doors and windows rad is now working she has just rang again the rads not working room is up to temperature I presume question is what would you do in this instance ?
Some TRV's have limiter stops. Use if there.
Others, you "can" often remove the cap and reposition it to achieve same result, so as the room cannot get too warm. Aim for 22 L.Room. or 20 elsewhere.
TRV's often stick, turn them fully closed, then open again, maybe a few times.
If this doesn't work, get them replaced, or stripped and cleaned by a plumber.