City water overfilling fresh tank

[DougW9876]

I added an external check valve from the local hardware store, to the outlet side of the pump.

It is better to add the extra check valve between the fresh tank and the pump, on the inlet side of the pump.

With the extra valve on the outlet side of the pump, if the pump check valve is leaking the pump valve will still leak down and the pump will kick on for a very, very, short time like 1/2 a second or less each time the water leaks back through the pump. With the check valve on the inlet side of the pump the water in the pump can’t leak back.

[Pap and Mimi]

It is better to add the extra check valve between the fresh tank and the pump, on the inlet side of the pump.

With the extra valve on the outlet side of the pump, if the pump check valve is leaking the pump valve will still leak down and the pump will kick on for a very, very, short time like 1/2 a second or less each time the water leaks back through the pump. With the check valve on the inlet side of the pump the water in the pump can’t leak back.

The valve that I purchased had a “pop off” pressure above what the pump would “pull” if it had been on the inlet side.
My little local hardware store didn’t have much of a selection.
It has been installed almost 2 years and has never cycled like you describe.