Other than a leaking 4 way selector valve the probable cause would be a leaking check valve in the pump.
On the RV the city water and discharge from the fresh water pump are tied together. When on city water the discharge of the pump will have city water pressure on it. If the internal check valve on the pump is leaking, water will flow through the pump backwards and into your fresh water tank.
Typically this requires ether replacing the pump or installing a secondary check valve between the fresh water tank and the pump suction.
634 views
Usually answered in minutes!
×