gas central heating - single radiator stopped working

Can someone clarify for me, are these easy to replace? Does one size fit all, so to speak, or do you have to get ones that go with your specific radiator?

Reply to
dustie
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TRVs are not specific to particular radiators, and are pretty much inter-changeable between makes *provided* you replace the whole valve - which requires a partial drain-down of the system.

If the 'wet' part of the valve is ok, and you simply want to replace the part containing the thermostatic capsule (which you can do *without* a drain-down) you need a thermostatic head for the specific type (make/model) of valve - they're *not* all the same.

Reply to
Roger Mills

Yes and no ;-)

When you buy a valve, it will come with a matching tail that screws into the radiator[1]. So you can always be sure of being able to get a good fit between rad and valve.

There are two other gottchas though. Firstly the spacing between valve and rad can vary (some modern valves like the Pegler Terrier II, have a free floating olive on the rad tail that lets you vary the actual length of the tail by about 10mm the first time you fit it. Sometimes you can fix a mismatch simply by shifting the rad on its mountings a little.

The second one, is the maximum depth of insertion of the 15mm pipe into the compression fitting is not always the same. Sometimes if you are unlucky, you can find a new valve won't make a good seal onto the pipe using the old olive and backnut. This can be fixed by replacing the olive though.

So in summary, if you are lucky, you can buy a new one, reuse the existing rad tail and pipe positions, and its just a like for like swap. If you are really unlucky, you need to change the tails, and tit about with the pipework.

[1] some are screwed with assistance of a spanner, others need a large Allen key stuffed up em. A good few turns of PTFE tape on thread first helps ensure a watertight fitting.
Reply to
John Rumm

I recently changed all mine & found the threads on the old pipework didn't match the threads on the new valves - almost nipped up, but not quite - so I had to change the nuts & olives.

Reply to
The Medway Handyman

I recently replaced all my (motley collection of) valves (both ends) for TRVs one end and end drain-off lockshields the other end. I had no problem with offsets - they were all close enough to fit without any pipework mods. [It would have been different had I used valves with the drain-off in the tail because these *do* increase the offset].

Yes, that *was* a problem in a few cases - the old olive was too far down the pipe to make a seal with the new valve. In one case, I cut a bit off the end of the pipe but mostly, I removed the olive and re-made the joint.

Another 'gottcha' which I discovered is that the threads are not the same on all compression nuts. Whereas most 15mm compression fittings have 1/2"BSP threads, some have a finer threads. In a few cases, I had to remove the compression nut and olive and replace them with the new ones.

But, as I said in my other post, if you replace the *whole* valve - including tail and compression nut/olive on the supply pipe - you can normally swap one valve for a different make/model with no problems. However, if swapping just the thermostatic head on a TRV, it *must* be the right one for the valve.

Reply to
Roger Mills

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