Hi guys, just wanted to ask a quick question regarding a low pressure Hwc before I call back there tomorrow.
I called to this property a month ago due to their vent pipe overflowing on their roof, the prv was ancient so I suggested a new one. I installed a new nefa 3.7 prv and also extended the vent on the roof, once I turned the water back on and adjusted the valve till it overflowed, then I wound it back, I found that no matter how far I wound the spring back out I couldn't get the vent to stop overflowing. I thought maybe some debris had passed into the new valve, so I checked the prv washer and flushed it out, no sign of any debris. I then adjusted the valve again and wound it back once it overflowed, everything seemed fine.....until today.

I quickly called by on my way home today after being informed the vent was overflowing constantly again. I had a quick look and found it was overflowing, I decreased the pressure and found the valve seemed to only fully shut off once the adjustment screw was almost completely out of the prv (the vent is more than long enough), I wanted to ask on here as I've never had this issue before and I'm hoping it's something simple which I'm just not picking up on.

In summary,
Low pressure cylinder, 3in1 valve before prv, then 20mm gate valve on cylinder. No temp valve.

Any ideas would be great, thanks in advance

Linkback: https://www.plumbers.nz/plumbing/1/prv-overflowing-issue/1886/

I had one with a cross connection, a European couple had joined the two hoses (hot and cold) together, with a Y connection, bought locally apparently.... and hooked it up to the one cold supply to where the old washing machine was. It only happened randomly when the European washing machine called for both supplies, real random.

Try isolating and checking how each appliance is hooked up.

Or it could be "creep", never come across it personally but I remember it from talking to a PRV sales rep, which could be a point of contact for you.

Let us know how you go mate.

hi guys, yeah had one similar where the client took off the rose of his `felton`mixer and put a ballvalve in, then rose into ballvalve to stop it dripping, took a while to find that but it cost him plenty,cheers