check valve between city water and water tank

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New member
Apr 14, 2019
I have a lance travel trailer 1685, I went on an extended trip, hooked up to water at camp grounds no problem, then my son had to fly and drive Trailer home because I hurt my arm, so him and his wife took a holiday also. When they came home and I hooked my water back to the trailer it made the regular water tank over fill, I think there is a valve that keeps this from happening? So now I'm  running off tank with pump that I have to turn on and off and the water pressure is useless if you want a shower, is there a fix for this?
Yes. You probably have a valve that's labeled tank fill. This valve may be partially open allowing water to fill your fresh water tank.
Another culprit could be a check valve at the water pump leaking by when you're hooked up to city water.
I had the exact same problem a few years ago on my last trailer and it was a defective check valve in the water pump.

Jack L
Two very good answers..
I have had the city fill valve left in half way position allowing water to flow into the tank both from city and from "house" pressure lines  the pump cycles on and off or stays on as water re-circulates when using the on board (Which I do full time now.. long story)  This is likely the first thing I'd check because fixing it costs $0.00 and that's my favorite repair cost.

Next is the valve can fail and not "Shut off" one or the other side.. This costs more but well you have valve options some are not that expensive (I really would prefer a different type of valve there but that too is another story)

Finally the pump check valve can fail. There are two of those so total failure is... Rare.
On my FW, the only way to fill the fresh tank is a "hole" to stick a hose in as part of the water hookup  panel.

The plumbing, simplified is this: 
Fresh tank --> pump - check valve -->TEE  -->to camper
Camp water --> check valve --> TEE --> to camper

Camp water is blocked at the pump check valve.
Pump water is blocked at the camp water inlet check valve.
John From Detroit said:
"Finally the pump check valve can fail. There are two of those so total failure is... Rare."

Please show me a diagram of where the second check valve in the pump is  ????????

Jack L
A pump will have a check valve on both sides of the pump head.  Look at it as a balloon.  As the balloon expands, Check valve 1 allows water in from the tank to fill the balloon while CV2 prevents drawing water from the camper back into the balloon.  As the balloon compresses, CV1 stops flow, forcing the water through CV2 into the camper plumbing.  These CV are usually built into the pump head.

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