The stem reducers are 10mm female end to 15mm male stem end - they are called reducers

I ended up getting the 10mm reducers, for the coupler as the 15mm were too big.The stem reducers are 10mm female end to 15mm male stem end - they are called reducers
I think I understand now yes the pipe is 10mm.The hot and cold supply pipes coming out the wall look like they are 10mm and the ISO valve is 15mm. So the female socket end of the reducing coupler is 10mm and the male end going into the ISO valve should be 15mm
Thank you yes saw the metal end and wasn't sure.No - As you can see from the end of the stem it has the ridges that act as the rumble end to ensure proper insertion, if it was going into another HEP push fit. That's why the inserts have those ridges so the fitting can be twisted and you feel the rumble of the fitting, that shows it's fitted all the way in.
No need for the insert as the stem end is thick enough



Yes I've had abit of a play and come up with this...I know it’s a pain, but could you redo the waste to be centre of the hep pipes?
I wasn't sure how to do it and would I have to drain the system? Or can i isolate the water and change them?You can change the whole valve to a black one, if that's what you mean. You can't just get any black TRV head and it's guaranteed to work, unfortunately TRV's aren't all made the same.
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