TRV thread sizes


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I have an old Drayton TRV 3 which has now broken. The new (replacement?) TRV 4 has a larger thread, which means I cannot simply replace the failed body.
Am I right in thinking that all new TRVs of any make now available will be the new size?
Can one still obtain new bodies in the old size thread?
If not, I guess I have to drain down the system and fit a complete new unit?
 
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Normal practice is to replace the whole valve. you should be able to disconnect from the 15mm compression nuts bottom and side and just swap the valve not the tails.
It would be very unusual for us to completely drain down the system to do this, probably take 20mins tops. with the loss of very little water unless in a very difficult position.
 
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I have an old Drayton TRV 3 which has now broken. The new (replacement?) TRV 4 has a larger thread, which means I cannot simply replace the failed body.
Am I right in thinking that all new TRVs of any make now available will be the new size?
Can one still obtain new bodies in the old size thread?
If not, I guess I have to drain down the system and fit a complete new unit?

(The above is dated 2012)

The two simple options are:-

1) Buy the same TRV3 on-line (auction sites), or other brand with the same thread.
2) Buy a "Thread Adaptor" - would suggest a steel one.

Note: There is a listing on the web* regarding "Adaptor List According to Valve Body Size". The only snag is it has the Drayton TRV3 listed twice
e.g. Thread Type M28 x 1.0 mm and M30 x 1.0mm -Adaptor available through other manufacturer - Imperial Thread.

PS Having the same snag - trying to fit a "Lightwaverf Smart TRV" (with two unsuitable plastic adapters) to a TRV3 gate/body. I have the M28 x 1.0mm Imperial Thread.

* https://energenie4u.co.uk/res/pdfs/Valve Adaptor List V5.pdf
 
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