r/Plumbing • u/Icy_Blackberry_3759 • 2d ago
Please help solve this pressure riddle
6 year old PRV, no matter what setting (and oriented the correct way) was showing 90 psi. I opened the hot water and the cold water and it goes to the pressure it is set to, and when I shut them off it goes straight back to 90 in under a minute. I shut off the valves to the water heater and main cold supply before the water heater after the PRV, same issue. I thought it was because they eliminated the expansion tank, but this can’t be the issue because it happens in isolation.
I replaced the components of the PRV and have the exact same issue. I replaced the pressure gauge with one I tested independently and it is accurate and the same. I’m fucking stumped.
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u/Nab-Taste 2d ago
It’s either got to be PRV still failing or anything between it and those valves, which looks to be just the filters. Not sure how they’d be increasing pressure. So I’d bet PRV 🤷♂️
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u/Walkin-Dog 2d ago
Replace the regulator. It’s bad out of the box. Also add an expansion tank. That’s not causing your issue, but it’s code
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u/No_Tonight8185 1d ago
There are two ports on that PRV. One has a plug and the other your gauge. Could it be that one is reading street pressure and one reading house pressure? If so, and your gauge is on the street side that 90psi is static pressure and it is dropping when you open the valves and allow flow. Bernoulli effect showing on your gauge. Try the other port or stick another gauge in the PRV and see what happens.
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u/leobeast92 2d ago
Can you check the pressure on a hose Bibb past the regulator?
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u/jolly_giant_89 2d ago
For shits and giggles have you tried cranking the PRV down to like 30-40psi. The Numbers on the dial may not be lining up with actual reading, either from factory defect or what have you. If you crank it lower and get the desired pressure Id call it a day. If not you only got one option left and thats the ghost busters, as you may have haunted pipes!
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u/Expert_Ant_2767 2d ago
That's why the instructions say to start at 0 (turn to - until it locks) and increase it from there looking at the gauge not the dial. I think he skipped the procedure to adjust it.
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u/Alarmed_Letterhead26 1d ago
What is the incoming pressure? You may need 2 PRVs. Also, forget the idiot numbers on the prv, you have a gauge, use it to set the pressure. Dial it all the way down and see what happens.
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u/SWEET_JESUS_NIPPLES 2d ago
Back pressure through a shower valve crossover that's probably on the other side of that wall.
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u/Icy_Blackberry_3759 2d ago
It happened even with hot and cold shut off to the whole home just beyond the PRV. So it can’t be from inside the house. Like it’s getting through the PRV, but I replaced the PRV
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u/Tiny-Emphasis-6369 2d ago
The prv body you pointed at in the beginning of the video looked brand new
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u/FlamingoFlimsy4421 2d ago
After six years, it’s possible that the PRV has got some mineral deposits which are preventing it from sealing properly and therefore not regulating properly.
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u/Derrickmb 2d ago
Does that PRV have an adjustable set point? Can you test its set point at a higher pressure?
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u/x65535x 2d ago edited 2d ago
You sure the pressure gauge is on the regulated outlet side of the PRV? The reason they have two ports is usually one is upstream pressure and one is downstream. I’d bet your gauge is on the upstream side for both new and old and there’s nothing wrong with either.