TRV heads - interchangeable? how to identify?

Question

I have a chrome TRV in the bathroom which isn't working - that is, it won't turn the valve off even if set to frost protect.

As an interim test I've swapped it with the one from the downstairs bathroom (no idea if this one works OK) but if the head of the TRV is duff, I would be looking for a replacement.

Looking back (via Homeowners Hub mea culpa) I see that most TRV heads are probably interchangeable. So far so good. However how do I confirm the brand and model.? These look like Drayton TRV4 Chrome but I can't at the moment see anywhere on the TRV head with a brand or model number.

Any obvious way apart from they look like the picture?

I will have to hunt around in the plumbing pile of bits to find a decorator's cap to confirm that the valve is shutting off.

Cheers

Dave R

alan_m · Accepted Answer

The pin in the body could be stuck or the head not completely seated. If the head is not completely seated downwards the expansion capsule in the head will have insufficient travel to push the pin in the body fully downward to switch off the valve.

Take the head off to reveal the pin in the body.

You should be able to move the pin down by a few mm and it should spring back

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Note: Twist the head to the maximum setting before fitting it back on to the body. On some TRV the head needs to be pushed down firmly before tightening it up with the screw ring.

If the radiator is hot it may take 30 minutes to cool after switching off the valve.

David · Answer

Thanks, but I have done the initial obvious things. Pins move on the upstairs and downstairs. I have followed procedure removing and replacing the TRVs.

What I really need is the two questions posed in the OP answered.

Regards

Dave R

AnthonyL · Answer

I'm not an expert but I've never bothered to try and replace any TRV with what was there before, I've just bought what was most convenient at the time, usually Screwfix or we have a plumbing merchant up the road.

They strike me as being fairly simple devices (assuming not internet connected) that just allow controlled movement of the pin in the valve.

I thought they were only decorative on the balancing side of the radiator and they are on the opposite side of the temperature valve. I've used pliers to adjust those making note of the initial position first just in case.

Hopefully an expert will come along and clarify/confirm everything.

Roger Mills · Answer

There are at least two different thread sizes used on different makes/models of TRV. When, for example, you buy a Hive smart radiator valve to replace an eixting TRV head, it is supplied with adapter rings

- and you have to select the correct one to fit the wet part of your valve.

The most common thread size is 30x1.5 (30mm diameter with a 1.5mm thread pitch). That's what all my Drayton TRV4s have.

If your TRVs are genuine Drayton TRV4s, it will say so on them. But there are also generic copies on the market which are unmarked but should be compatible.

alan_m · Answer

One of te other smart radiator valve manufacturers also confirms this by saying their heads  "fit almost any valves directly or with adapter" and supply 4/5 different adapter rings.

David · Answer

Perhaps that is the answer.They may be copies.Anyway, generic one ordered as the fault moved with the TRV.CheersDave R

Pamela · Answer

On our TRV heads (Tower TRV2, not Drayton) there is the tiniest lettering of the model number to be found the underside near the screw threads. It needs a magnifying glass and bright light to read.

Pamela · Answer

Were you the poster many months ago who suspected their TRVs caused a clicking sound?

David · Answer

No

David · Answer

Brief update:New generic TRV from Amazon.Fitted and working fine.Haven't bothered testing until now because the CH has been off, but yesterday was chilly so I turned the heating back on.CheersDave R

TRV heads - interchangeable? how to identify?

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