Fred coughed up some electrons that declared:

Hi,

I've got a radiator that is not warming up and I think the TRV is
stuck. I know this happens now and again. If you take the top off,
there is a pin. I can't remember, do I push it in or pull it out to
release it?

Would a little 3-in-1 or WD40 on it prevent this happening again?

Thanks.

Just dealt with two such stuck valves. Take the head off (the dry bit only),
then see if you and push the pin in (not too hard mind).

If not, try a sharp tap with a light metal tool, eg pliers or pin hammer.
You are looking to invoke a small shock to crack the stuck valve open, not
to hit it so hard you damage it, or upset the compression/screw fittings.

Worked on both of mine. Then put the head back and turn on and off a few
time, which should finish the job.

If that doesn't work, don't get any more violent or you might get wet, in a
black yukky magnetity sort of way. Buy a new valve and fit when convenient.

Cheers

Tim