Fresh Water Tank Filling Up

I usually use the water pump and tank as well but leave the city water on so i just have to move the switch on the rig to fill the tank again. I have replaced the o-rings on the valve to switch between fill and flow.

Either pump internal check valve is leaking allowing city water to backflow thru pump
OR
'Fill' valve is leaking thru

Fill up fresh water tank.....turn off city water source and use pump
Flow thru pump may clear check valve (diaphragm) of any scale/debris


After using tank of water with pump....swap back to city water if you wish.

I always use pump/tank.
Flooded rig one night while sleeping on city water and fitting broke...$6000
Since then.....pump/tank and just fill tank as needed
Easy to turn pump off when sleeping, going outside, leaving cg etc.

Probably a bad check valve at the pump.