Trv not turning off heat to radiator

[Giulia]

Hi,
have a new house and all my radiators have Myson trvs on them and work fine except for one.
I purchased a Myson trv for it thinking they all would use the same and it seems to fit OK but when the heating is on and the trv is turned off,
the radiator still heats up as if it was turned on full.
(The trv is new and I swapped I for one I know was working so I know it works on another radiator)

Here are pictures of it.
On the left side covered in paint and hard to read looks like it says Pegler terrier. It has a screw in the middle of it
- is this the lockshield valve?
On the right of the radiator is the pic of the one with the pin showing
- this is where I tried the trv, is that the correct place?
I took the trv off and checked that the pin does go down and up again
- should it go down flush? (I'm not sure that it goes totally flat down but it does move up and down somewhat. )

- I'm curious whether having one side pegler means that the other side should be a pegler trv?
Would that make any difference or is something else amiss?

Thanks, any help with answers is greatly appreciated

 

[Stuckinarut]

Yes the pegler valve is a lockshield/wheel head. When you say a new trv - the whole valve or just the head?

 

[Giulia]

Ah yes just the trv head is new

 

[dilalio]

Tap the pin gently a few times with a hammer. You should feel a spring resistance to it.

 

[Stuckinarut]

Ah yes just the trv head is new

As per @dilalio the pin will be stuck

 

[Giulia]

Thanks for this.
it's going down and I feel the spring resistance. I'll check how far it should go down on another radiator
that is working. Thanks.
If that doesn't fix it does it mean there's something wrong internally?
Thank you

 

[terryplumb]

Yes ,Change the whole valve for a new one.

 

[dilalio]

Yep. As above.