MDPE to stopcock leaks!

[Tipper]

I have been having trouble getting a reliable joint between the blue 25mm MDPE incoming main and the 22mm stopcock.
The first issue is the SWWater supply pressure which is 12bar!
The second issue is the transition fitting from MDPE to copper before the stopcock and the pressure reducing valve.
I first had a blue pushfit to female thread plus compression copper fitting and then a short length of copper pipe before the PRV. This connection failed after a few months due to the plastic thread distorting and no amount of sealant or tape on the thread would hold.
Changed the fitting to push fit blue to push fit on to the copper, this too now leaks at the copper end after about 6 months.
How can I get a good leakproof joint between these two pipes? Is there another way of achieving this transition?

I'm fed up with constantly having to redo this joint. Any ideas?

 

[leakydave]

Have you tried a 25mm to 22mm brass stop tap then PRV and DOC

 

[Charnwood]

It is definitely blue, metric MDPE you are connecting to, and you are using an insert?

 

[Tipper]

Have you tried a 25mm to 22mm brass stop tap then PRV and DOC

That might do it, thanks

 

[Tipper]

It is definitely blue, metric MDPE you are connecting to, and you are using an insert?

Yes, new pipe only 4 years ago and inserts used throughout but it's not that joint or any other blue joints that leak!

It looks like converting to 22mm before the stop valve was the stupid plumbers choice! I'll go with the above suggestion unless someone has a better idea.

Interestingly there are 2 other similarly configured joints (3 flats in all converted at the same time) and the other two have been fine....touches head!!

Thanks guys.