We have a Zurn NR3XL PRV that's less than 3 years old, but according to the plumber that was here recently it's gone bad. His reasoning was hooking up a water pressure valve to the spigot, and it read like 125psi. I had mentioned it had been turned all the way up to max allowable pressure during installation by the same company (and later the adjustment screw was turned 100% tight clockwise by a different contractor doing a bathroom remodel that forgot to adjust back and it needed backed out). The current plumber last week stated it doesn't matter; the operating max pressure is 75lbs, so even if fully adjusted to max PSI it still shouldn't read that high.
That does make sense, but I had to see myself as the PRV isn't old. I got a water pressure tester and prior to adjusting it back out, I took this reading (BTW I opened spigot to let run, then shut off, then placed valve to read as Zurn recommends to let initial pressure flow). Indeed too high: measured around 115psi.
Next I backed it out several turns (like 10-15). Took a new reading and now I was seeing much lower as expected around 55psi.
I screwed it back in as that's a bit low for the house and now it's around 65psi.
So the adjustment seems to be working as expected. What I wonder is if the adjustment screw is fully tightened maybe the valve acts as a pass-through letting supply side sigh pressures straight through and this is normal behavior? Or was the plumber correct in that no matter how much the adjustment screw is tightened down on the PRV, it should never allow more than 75psi, indicating some sort of failure? I've already bought a replacement (figured out correct part from this post here), but it's silly to be to replace it if this is all expected behavior and the fact that the pressure is way down since I adjusted it back out, maybe I do not need to replace the PRV?
Looking at the behavior is this all normal and no need to replace the PRV, or is the fact it initially was so high a concern and I should change it out? Also as an aside the red needle would spike only initially when turning on the spigot initially but never consistently was that high, inquiring if that's normal too?
Here are the pressures at various times over the last 48 hours. Notice there is a bit of fluctuation. I know the PRV isn't responsible for an keeping an exact finite psi value but some of this seems kind of wide. Is this an indication of a failed PRV? Also looked into thermal expansion but the tank is practically brand new.