A pressure regulator is meant to hold (regulate) the downstream pressure
when there is flow. When the system is shut down (faucet closed) the
regulator shuts down also. If the system pressure rises to the upstream
level it would mean (in my opinion) that there is some leakage past the
shutoff seals. To be sure, one would need a schematic of the regulating
valve to understand just how it works. Most regulators have a differential

flow or no flow a regulator maintains the it's set for. go to home depot & in
the sprinkler area they have little pressure guages for 10.00 BEFORE the
pressure regulator take a reading (at your meter u should have some little
threaded openings w/ little valve lever on the anti syphon valve) take a
reading, then AFTER the regulator find a spot and take a reading. But i can
guarentee you the regulator is slowly bypassing water. they're made of brass
and soft the seat or the seal surface has cecome imperfect and is leaking.