Radiator valve size

18 Jan 2023
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United Kingdom
Recently moved to a new house and need to change the radiator valve in the bathroom as its leaking.

Am unsure of the size as the pipe coming into the radiator are much thicker than normal(Picture attached).

The incoming pipe is 70mm in circumference and the pipe between the valve and the radiator is 90mm in circumference.

Any help will be appreciated.


  • Radiator Valve Bathroom.JPG
    Radiator Valve Bathroom.JPG
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It's a lockshield valve with 3/4 union fitting to tail ,and 15mm compression to supply pipe.
Your measurement are way out by about ten fold !!
70mm circumference would not equate to a 15mm diameter pipe ,that's more like 22mm. Re check your measurement.
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its not a 15mm for sure, the other pipes in the house are 15mm and this is much thicker.

22mm sounds right, but do I need to worry about the side where it joins the radiator ?
Yes ,the tail ( the part that goes into the radiator) would be part of the new valve, and obviously has to be the same thread pattern as the rads inlet port.
Your supply pipe may even be old 3/4 inch ,is it an old property ?
Your best bet would be to take the valve and its tail ,to a reputable plumbers merchant to try to match like for like.

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