Onboard pump forcing fresh water out the water inlet – Help!

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gary-736Dear Gary,
My 29-foot Dutchmen Class C is parked under my pole barn and it’s plugged in for power but nothing else is hooked up. When I turn on the water pump, it pumps gallons of fresh water out through the park water hose inlet and emptying my fresh water tank. When I turn the pump off, it stops. The pump is only a few years old. I would appreciate any guidance. Thanks! —Jim M.

Dear Jim,
Onboard pump forcing fresh water out the water inlet – Help!All RVs have at least two backflow preventers (check valves) in the fresh water plumbing system. Some RVs have three and some even have four backflow preventers. Every RV has one at the city water inlet which allows water to flow from the campground into the RV. The backflow preventer at the city water inlet has obviously failed in the open position. It will have to be replaced, or at least a new one installed right behind the existing one.


Since it failed in the open position, it’s not really necessary to remove it (though it’s advisable if you can). A new backflow preventer can simply be installed just inboard (downstream) of the old one. That will prohibit water pushed by the onboard pump to be forced out the city water inlet. Actually, it’s not a difficult task for the average handyman to accomplish in a few minutes –once you gain access to the rear of the existing check valve.

Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.

##RVT860;##RVDT1190

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Gene Bjerke

I had that happen in the middle of the night while on the road. I effected a temporary fix by sticking a cork into the inlet. That worked until I got home and had a new check valve installed.

Tommy B

My brand new camper did that 2 weeks after I bought it. I went to a hardware store and bought a plastic plug( male) and screwed it in and no more water blowing out until I could buy and replace the inlet old one, plastic. New one brass $21 Amazon. Old cr** probably.35 cents.

Leo Suarez

I had the exact same problem, and it turned out that my rig has a small remove able mesh filter at the city water intake. It is shaped like a small cone, the size of a thimble. Turns out I had removed it to clear some debris which it had effectively caught, and I put it back with pointy end of cone towards the RV. That pointy end pushed the back flow inverter valve enough to cause the problem. I flipped the screen (pointy end towards me) and problem went away.