Faulty TRV head or fault plumber?

[Woby Tide]

I've searched around a bit but most queries regarding broken TRV's are in reverse where the radiator is cold due to the pin being stuck. Does it also happen in reverse? We have 3 or 4 radiators fitted with TRV's that remain permanently hot regardless of where the TRV is set too. The remaining radiators fitted with TRV's all work fine and can shut off accordingly.

I guess removing all the heads to see if the pin is stuck permanently on is first port of call but is it likely that 3 or 4 would fail with exactly the same issue at the same time or is the whole unit likely to need replacing as valve (or whatever restricts the flow) is broken?

(At an outside guess could the TRV's have been installed on wrong side of radiator, but surely that would be exceptionally unlikely? They were installed some tme in last 10 years and I think it's likely to have been done by plumber as whole system was replaced during an extension build so likely to have been a 'proper' plumber rather than DIY)

[TMC]

Fitting wrong end would not prevent the valve closing.

2 possibilities 1) plunger inside has jammed open..... remove head and test body by pushing plunger down manually 2) Head is no longer working..... swop with one that is on another rad to confirm

Tony

[chris_doran]

Re (2): To test the head, take it off and invert it. In the centre you will see the pusher that moves the pin down. Note the position, stand the head in a hot or cold place for a few minutes and see if the pusher moves. It only moves a few mm, so make it a significant temperature change.

2 more possibilities, especially if the head wobbles about:-

3) Ring screwing head to body of valve is loose. Open TRV fully and screw it down -- Finger-tight will do -- then reset the TRV.

4) Rim on head which engages with said ring is broken, so it won't tighten down. A bad explanation, but will be obvious when you try to screw it up.

I have a lot of Landis & Gyrs which are notorious in respect of (4). The rim is on the end of flexible fingers which are easily snapped off if the head gets a bash. My own question: Does anyone know where I can get replacement L&G or compatible heads (SE London)? Wickes and Homebase don't seem to have them and the chap in Plumb Misspelled barely looked up from the counter when I asked (do you have to wear greasy overalls to get attention?).

Chris