Fresh h2o backing up and overflowing fresh h2o holding tank

One other low-tech possibility -- if the flexible fill tubes run under the dinette seats, and if someone has put bulky cargo items into the storage hatch below the seat, and if that cargo bends the fill tube upward, then water may shoot out of that fill tube when you are trying to fill your tank, thus soaking your pants.

Remove the offending cargo and try it again after changing your pants.

Please don't ask how I know this.

When I’ve had this happen before it was the check valve in the water pump failing. Solution can be to take it apart and clean the pump. The first time it happened to me the dealer just replaced the pump under warranty.

How do you FILL fresh water tank
Gravity fill port
OR
FILL Valve that you swap from City Water/Normal to FILL position ??


Fill Valve...
They can fail (o-ring) or leak thru

Pump has an internal 'check valve' (diaphragm) that can fail/get held open
Some times just running /using pump will clear any debris on diaphragm and allow it to fully close

***With City Water OFF/Pump ON but all faucets off....listen for pump to run short cycles
Check Valve leaking the pump will turn on when pressure goes down then turn right back off when pressure is restored.

Fill valve.....pump may have hard time developing full pressure. May take longer to turn off when faucets are closed

If you have easy access to pump suction side...disconnect the pump suction line.
Turn on city water supply and see if water comes out of pump suction side

Do you have a Showermiser? If it is on the city water can overflow the fresh tank. Mine has a warning label.

Turn city water off, then make sure you open all faucets hot and cold side and run water pump to get air completely out. Then shut off and open city water again. There’s some YouTube videos out there on it and worked for me recently when faced with same problem.

It could just have junk stuck in it.

Yes there is.

When I hook my 5th wheel up to water supply the water backs up into the fresh water holding tank until it overflows. Anyone know the cause or fix? Is there a check valve in the 12volt water pump that has failed?