Andy Burns wrote:

I brought the PRV home, no accessible parts, can't blow or suck through it

Put it on my garden tap, heard it gave a "click" and water started
flowing, here it's on 15mm pipe and 1/2" tap, there it was on 25mm pipe
and 3/4" tap, pressure on both is ~2.5 bar.

Having removed it again you can suck and blow through it now, seems that
the valve locking-up as per the amazon reviews is real.

Maybe it doesn't like having to feed 50m of empty pipe? Though actually
I did try it with nothing on the output after it had originally failed,
so why did it "reset" itself?