PRV fault

[BPM]

Does anyone have any experience in failing PRVs?
in my property in France, I have a Sauter 200l electric wall hung water heater. The inlet PRV on the old heater kept letting by. Found another PRV on the incoming main. The main PRV showed 2 bar on the gauge which is clearly wrong. Took it apart and put it back together. Adjusted the incoming pressure to the meter to try and get more pressure in the house. I should mention that the start to all this was almost zero water pressure coming to the house. I know the main supply pressure is ok because there's a separate supply going off of the main before the first PRV and the pressure was fine.
Turned up the pressure, all good to the house but the water heater PRV then let by. PRV is rated at 7bar and there's clearly not that much getting to any tap!
so, changed the PRV, no improvement. Took the opportunity to replace the old water heater and fitted a brand new PRV which was an exact 7bar item to the old one. Turned the water on, instantly let by. Turned off the water main and put back on a quarter turn only. Almost nothing to the taps but the water heater PRV let by instantly.
Essentially, no matter how little pressure is coming from the main, the PRV releases. Same on the new one as was on the old one. Could these French units have a quirk that once they let by they don't actually ever reset again?
not quite sure where to go next, different make of PRV perhaps? I've never had an issue in the UK with any I've fitted but I'm not 100% on anything non UK

Any my help much appreciated on any ideas, I know this is a question not about the UK but the principals remain the same I assume.

 

[WHPES]

Would probably try another. They should be automatically resettable. When you say passing, do you mean releasing or just leaking?

 

[Unregistered]

Passing as in pretty much letting all the incoming water instantly come out of the relief valve. It's not appearing to now be releasing based on a pressure build up but more that it just simply can't hold the water at all. Seems rather odd that this second one has the same issue as the first yet neither are on the same heater since its been changed.
the prv does appear to operate in that you can turn it to test its operation and it closes back off as it should, but literally a couple of seconds later it starts to stream out. I think it has to just be bad luck and a faulty second valve?

 

[Dotty]

You have another problem. I'm not sure what the regulations are in France with regards to unvented cylinders but we can only apply what we know over here.

Which is stop playing with it and get someone in who knows what they're doing.

Job 38.11