TRV closing almost fully even on max

[johnny2007]

Hi, the other day I realised one of the radiators was staying lukewarm.
I opened fully the trv (drayton trv4) and still same.
When I unscrewed the trv head, I heard water flowing in the radiator and it got hot very quickly.
Radiator works perfectly without it.
Checked the pin and it moves freely.
So I tried to screw back the trv head and realised that it start pushing the pin down even before I start screwing it in.
In other words, when I fit the head, it pushes the pin down and blocks the flow.
Is there an adjustment or something that has moved or is it a faulty valve head?

 

[oldbuffer]

Was the head set to max temperature when you tried to screw it on?

 

[johnny2007]

Was the head set to max temperature when you tried to screw it on?

Yes

 

[Madrab]

a faulty valve head

 

[johnny2007]

I see.
Thanks, but how has it gone wrong?
It's worked for a number of years but it looks like it's lost the full open setting.
I mean, the plastic bit that pushes the pin down has changed position?
I don't understand how that is possible

 

[Johntheo5]

Does the actuating pin move in and out when you watch it with the actuating head in your hand when you turn it in and out.?

 

[johnny2007]

Does the actuating pin move in and out when you watch it with the actuating head in your hand when you turn it in and out.?

Yes, as i turn the head from max to min and vice versa it moves up and down

 

[Johntheo5]

Can you swap heads from another rad.?

 

[johnny2007]

Can you swap heads from another rad.?

Yes, I'll try that tomorrow and report back.
Thanks.

 

[Madrab]

Sometime the vial inside, be it wax or liquid gets jammed or burst and no longer expands or contracts.

As suggested, trying another will confirm

 

[johnny2007]

Ok, I tried another head and it's the same.
Then, on cold radiator I refitted the original one and the pin is not pushed down.
Until the radiator gets hot, then the pin seems to expand and partially closing the valve.
Removing the head opens the valve fully.
This happens with both trv heads.
Is it the valve itself that is faulty?

 

[Johntheo5]

To check if valve pin expands/extends with heat you need a vernier calipers to check cold length vs hot length.

 

[johnny2007]

To check if valve pin expands/extends with heat you need a vernier calipers to check cold length vs hot length.

Will check.
I suppose it must not expand as much as closing the valve, correct?

 

[Johntheo5]

If you are talking about the actual valve pin in the valve body then I would expect little or no extension with rising temperature, its just a spring loaded valve.

 

[Madrab]

That's a strange on as the trv valve itself isn't complicated and there's very little to go wrong. Is it the TYRV end or the lockshield end of the rad that heats up first from cold?