Stone cold radiator, not full of air, TRV isn't stuck.

[cantab]

I have one stone cold radiator when the heating is on. I bled it, no air escaped. Bled most of the other radiators, a load of air escaped from one (the one with the highest top edge, if that's significant). I removed the TRV head and pushed the pin, it wasn't stuck.

What else might cause this problem?

 

[kevplumb]

lockshield closed

 

[eastyorksman]

shut all your other rads trvs and see if that makes the offending rad get warm, could possibly be an air lock in either the flow or return to that one rad if it is a down stairs one.

 

[cantab]

What's the lockshield?

Edit: Upstairs radiator. Downstairs back boiler.

The inlet pipe is warming up. So maybe the inlet valve is more badly broken?

 

[kevplumb]

valve on the other end

 

[cantab]

YES! That worked! Took the cover off and gave it about 1 turn anticlockwise, and it's heated straight up.

'Course, I've probably gone and thrown the system out of balance.