Simple way to determine which is leaking......fill valve or internal check valve in pump
Remove pump suction line at pump and see it water comes back thru pump
No....then fill valve is leaking thru. Anderson valve?
Yes.then pump check valve is leaking thru. Turn off city water and use pump (complete fresh water tank) and then see if pump still leaks thru when you go back on city water.
As 'DrewE' pointed out.........in-line check valve install on suction line for pump
We don't use the city water.
We fill fresh water tank and use pump
No overfilling of tank
Pump provides all the pressure needed
Pump short cycles indicates a leak.......which I then know about and can find/fix