Water water everywhere

[basqueman]

I've had my 3810ms for 6 years and never had a problem with my city water hookup. Trailer at a nearby rv park and we went back home last Sunday. Water turned off at hydrant and disconnected from line like we have done for years. Came back today and reconnected the hose and turned on the park water. As I walked back to the trailer I heard water running outside and saw water coming out the rear overfill. Ran to command center and the valve was set to fresh water not tank fill. Water still pouring out. Turned to tank fill and water flow increased. Turned back to city water and water still flowed. HELP.
My assumption is that in 4 days somehow the valve behind the command center simply failed with no water or pressure behind it. How's my guess and how to fix it?

[rohrmann]

It's the check valve in the water pump that is allowing water to flow into the fresh tank. Depending on which pump you have, the check valve may hang on the outside or it may be internal, but in either case, there may be debris causing it to not seal or the seal has failed. I had that problem years ago and fixed it by installing an inline check valve in the PEX on the pressure side of the pump. In the photo, it is the brass device in the lower center.