[Richard]

The one I listed and the first one you listed are one and the same. It doesn’t make sense that the first one would migrate overnight unless you have debris in the lines. I apologize that I misinterpreted “I could see”. On second read it is clear what you meant.

I am just as puzzled as you since the first regulator should not have drifted.

Just out of curiosity, did it return to 20 psi when you would flush the toilet. That is after creeping to 55 overnight?

I can think of one bizarre scenario, and it would be easy to check for. The bizarre scenario is that the air pressure from the flush handle is leaking, leaking into the sequence valve, and providing back pressure to the water overnight. You could deadhead the pressure regulator with a cap and test to see if it is truly migrating or the pressure is coming from the air system.

A pressure regulator only works in one direction. If the pressure downstream on the regulator increases for whatever reason, the regulator will not decrease the pressure to the setpoint.