Watts Pressure regulator does not hold water pressure
I have a Watts 1 inch pressure regulator (series 25AUB) in an outdoor underground pit (about 3.5 feet below the surface) that was installed in 2005. The regulator is used to drop the city supply pressure which ranges from 100 to 130 PSI (as measured at the water meter) to a pressure of about 40 PSI (as measured in my basement). About a week ago the water utility repaired a main line leak about 1/2 mile from my house and had the water shut for about 4 hours. Ever since this repair, the regulator no longer holds the pressure to 40 PSI. When I go to sleep the pressure is at 40 PSI but overnight the pressure creeps up to about 60 PSI. I did an experiment last night where I isolated the hot water tank (by closing the inlet valve) from the cold water supply. The pressure this morning still had increased to about 60 PSI which means the pressure increase is not due to thermal expansion from the hot water tank.
Why can't the regulator hold the pressure? Could this be due to dirt on the seat where the dirt was introduced into the system by the utility's repair? If so, is there a way to flush the dirt without taking apart the regulator? Is there another possible cause? Do I need to replace the regulator?
Should I ignore the problem or is the regulator about to fail and should be replaced?