Interesting issue

[gscudder]

Ok,
So this is gonna sound crazy, but this morning my freshwater holding tank decided to fill itself! Around 1030 this morning at the campground in Tucson after a chilly 28 degree night my wife informs me that our freshwater tanks are overflowing. I instantly go to the utillity compartment and the tank-fill is not on. I have the wife shut off the water at the hydrant and dump about 1/4 of the freahwater tank and continue to run our dishwasher on the internal water pump. A couple hours later we return everything to normal and, no issue. Its like it never happened?
Just for informational purposes we have a 2014 Fleetwood Discovery class A.

[DutchmenSport]

Dutch_12078 wrote:
My guess would be that ice formed in the pump and held the internal check valve open. That would allow the city water supply to backfeed into the tank. When the ice melted, back to normal.

This was *exactly* my first though too when I read your post. Ice formed on the pump check valve keeping it open. Later, it thawed enough to function properly.

Just curious, is your on-board water pump in a warm compartment, or exposed to the cold?

[Old-Biscuit]

Real good chance is was the internal check valve in pump.
Running pump cleared the internals.

[dbbls]

Either the check valve was stuck or the Anderson valve is leaking letting water into the tank.

[Dutch_12078]

My guess would be that ice formed in the pump and held the internal check valve open. That would allow the city water supply to backfeed into the tank. When the ice melted, back to normal.