How does this radiator valve work?

[mr_tumnus]

Hi folks,

Minor mishap, just cracked the head off a thermostatic valve. I've removed the head unit and this is what I see:

From pratting about on the internet, this looked to be a straightforward fix, simply buy a replacement head, screw it in, bob's your uncle. A couple of unexpected discoveries, though:

1. The pin does not drop. I've given it some WD-40 to release and some taps and it is not budging. I may be wrong but this does not feel designed to move.
2. The black plastic collar surrounding the pin screws in and out, lowering and rising as it does. It's numbered and has a notch cut into it (marked on the photo) which presumably mates with the head unit, although it's not very obvious to me how the now-broken head achieved this.
3. If I turn the black collar using a flathead screwdriver and the notch, this opens and closes the valve manually - at least I think so.

I may be being dense but given the pin seems to not move at all, and I'm not certain it ever did, I'm not sure how the thermostatic head would ever have actuated it.

Can anyone illuminate me as to what I'm looking at and, if possible, tell me what I replacement head is compatible with the valve?

Thanks in advance.

 

[kidgreen61]

If the pin is seized solid, you will need to replace the entire valve, bear in mind those pins only move a couple of mm anyway.
try to press it down with something soild to see if there's any movement, if not, GENTLY try to ease it up with some pliers.
I swear TRV's cause more problems than they are worth.

 

[Mister Banks]

The valve can be used to balance the radiator but virtually no one does so just leave the valve on the highest setting and use the lockshield for balancing the radiator.

The pin is meant to move so you will need to free it or replace the valve.

 

[mr_tumnus]

Thanks for the replies, both.