Fresh water tank keeps filling

I have had to open winterizing valve to suck air into line to clear check valve

I love it when someone posts an answer and that works.

Took your advice, ran the pump for a few minutes, then drained the fresh water tank. So far it hasn't filled up again. Perhaps some debris was clogging the check valve.

I got tired of mine doing the same thing and added a check valve between the pump and tank

Yep, only 2 ways for this to happen. Fill selector valve is leaking or the check valve on the water pump is leaking by and back-filling the fresh tank. Best scenario is if it's the check valve, as it can often clear with use. If not, then you need to get it to a dealer for warranty service.

Lyle

IF you have a 'Fill' setting that valve may be leaking thru

Pump internal check valve may be leaking allowing back flow thru pump


With city water connected...set to supply rig
Disconnect pump suction line and check if water flows out of pump.
No water flowing then 'Fill' valve is not fully closing/leaking thru
Water flowing out of pump....then pump check valve leaking

Fill valve......exercise lever, lever may be slipping on valve stem, valve may be sticking, valve may need replaced

Pump check valve......fill fresh water tank, disconnect city water and USE pump
Flow thru pump may cleaning debris/scale on diaphragm and allow it to fully seat
If when using pump and pump cycles w/o demand then check valve is still leaking
Warranty time......

It is probably some dirt(from manufacturing) in the check valve of the pump. Run the pump for a few minutes and get some clean water thru it and see if this helps. If it was valves set incorrectly it should fill completely in a few minutes.