We have 2001 34' jayco 5th wheel. We've had it for several years. Driven all over the US in it. Suddenly the fresh water tank magically fills itself. Disclaimer, I'm more than a handy guy. The only way to fill our fresh water tank, that I can see, is from the outside of the rv in the snorkel opening or from u dear the back bunk where the winterize tube, there's a valve there which I could turn on and fill it. It's off and doesn't appear to be leaking. Last night my wife was bathing the kids in the tub, which has no leaks I could see through the access panel and I noticed water coming out of the overflow drains under the fresh tank. I checked the tank level and the thing is max full. I have used the tank while driving and never fill it more than halfway as draining it takes forever. Has anyone ever seen/had/heard of this happening before? I'm thinking there must be a leak somewhere that is filling the case that covers the fresh water tank and filling the tank to capacity and then over flowing. I don't want to over react and start taking everything apart if I am just missing something obvious.

I quick note the filling thing seems to happen abruptly as opposed to over a long period of time.

Either the fresh water tank/water pump or the shore water supply can feed your RV's plumbing system. Therefore, both lines will have check valves to prevent backflow when the alternate source is being used. It sounds like the check valve in the fresh water tank/water pump circuit has begun to leak by, thus allowing shore water to reverse flow into the fresh water tank.Rusty

the check valve on the water pump has failed

There is a check valve in your pump might want to give that a look and make sure it is working.

sounds like the checkvalve on the upstream side of your pump where the tank line connects. If that fails or leaks, city water fills the tank.

Fresh water tank magically fills itself | Good Sam Community

atxshaws
Explorer
May 06, 2015
I quick note the filling thing seems to happen abruptly as opposed to over a long period of time.
RustyJC
Explorer
May 06, 2015
Either the fresh water tank/water pump or the shore water supply can feed your RV's plumbing system. Therefore, both lines will have check valves to prevent backflow when the alternate source is being used. It sounds like the check valve in the fresh water tank/water pump circuit has begun to leak by, thus allowing shore water to reverse flow into the fresh water tank.

Rusty
newman_fulltime
Explorer II
May 06, 2015
the check valve on the water pump has failed
Toddupton
Explorer
May 06, 2015
There is a check valve in your pump might want to give that a look and make sure it is working.
Mile_High
Explorer
May 06, 2015
sounds like the checkvalve on the upstream side of your pump where the tank line connects. If that fails or leaks, city water fills the tank.
The_Texan
Explorer
May 06, 2015
Been there done that, your check valve on the water pump has failed.
Greene728
Explorer
May 06, 2015
Yep. Bad check valve.
RoyB
Explorer II
May 06, 2015
Here is a typical water flow pictorial showing how the RV water system works.

Sounds like a malfunctioning one way water valve between the fresh water tank and the pump. Some pumps have this feature built-in the water pump itself..

If you can find the one-way valve you might be able to clean out some debris and make it work correctly again...

Roy Ken
djousma
Explorer
May 06, 2015
It's worth noting that when the built-in check valve in the pump fails, there is no way to "check it", really. You could pull the pump apart and examine the diaphragm for debris. You can usually buy replacement diaphragms for the pump, or just replace the entire pump. But the check valve is part of the diaphragm design. I wouldnt add an additional check valve in-line, as it is just a matter of time where the pump stops pumping all together.
atxshaws
Explorer
May 06, 2015
Thanks all! I'll start checking those check valves out!