Cold rad

Im a 2nd year apprentice and my girlfriends radiator isnt heating up at all.It just happened out of the blue was working fine the day before.I went down the other nite and started to balance the rads down a bit and the rad did start to heat a bit but as soon as i turned the other rads back up the heat went out of the cold 1.I spoke to my boss he said to check the thermostatic valve as they sometimes give problems i took the head off and the pin wasnt moving so i pulled it out and put it back in a couple of times put the head back on and still no heat.Do u think i need to put a new valve on just its a danfoss 1.The pipe and valve the other side of the rad are hot but the pipe going into the thermostatic valve is completly cold.Ive blead it and there is water coming out so im kind of puzzled any help appreciated thanks.

It`s the thermostatic valve although the pin moves when pulled the actual valve seating is stuck. Most danfoss valves can be freed without draining, all you will get is a small dribble. Hve a small electicians screw driver handy .Remove gland nut that pin passes through and you will see a hole that pin sits in put screw driver into this give it a wiggle and it should pop out with a little bit of water replace gland nut and all should be ok. Other way is to give pin a couple of small hits and it sometimes frees valve seating

I was going to ask about this but having read this I no longer need to. Thank you indeed, fixed my lad's radiator and he's nice and warm now, we're both very grateful

Jeremy