Fresh water tank magically fills itself

[atxshaws]

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.

[atxshaws]

Yep. For now I turned off the valve on the suction side. I'll be picking up the check valve on Saturday. I pulled the electric from the pump so no one turns on the pump while it's out of service. I think that cheap fix will get us through the summer trip and I'll mess with the pump replacement once I'm back home. Thanks to everyone. Another mystery solved. Rv.net is awesome!

[golf_bears]

I think this may already have been covered in a few of the above comments.

There's only two ways to get water into the fresh water tank.

One, you connected one end of a hose to city water and the other end to the fresh water tank fill port. This is the normal way to fill the water tank.

The second way, which should not happen, is you're connected to city water and the check valve in the water pump is leaking and allowing water to back flow into the fresh water tank.

It isn't any more complicated than that.

So base on what you have posted, the check valve in the water pump is leaking.

If you don't want to replace the water pump then just put a check valve in the water line on the input (suction) side of the pump. Make sure you point it in the correct direction.

Let us know what you decide to do.

[djousma]

The other symptoms you would notice is if you are on tank water supply, and leave the pump on that it will "cycle on/off" when no water faucets are turned on. Same situation, in-pump check valve failing. another indication is that over time, the pump will be less effective (less pressure), as instead of pumping all the water it can, some is going back too.

[Big_Dog2]

I "tested" the check valve in the water pump in the following manner: I pressurized the water system (in your case you can just hook up to the city water) then disconnected the water tank to water pump hose (disconnected at the water pump). I then attached a clear plastic hose to the water pump inlet. I actually used the hose commonly used for sucking up the antifreeze when winterizing (in the old days when the winterizing hoses were not plumbed and valved in). I taped the hose in a vertical position then left it for a while. In my case there was some water in this hose so I just marked the level of the water in the hose. When I returned a short time later, the water level had risen several inches and I knew the check valve was leaking. Simple but worked for me. Hope this helps and you don't buy a new water pump if it is not necessary.

[atxshaws]

What's the thought on buying a check valve to put on that flex line that should suck water out of the tank instead of filling it? $8 for a brass version at Lowes. If it failed and my pump completely failed then I'd have the same problem, but seems like a good inexpensive fix/insurance for while I'm on the road this summer.

[atxshaws]

Thanks rusty. I've been under the bunk and I see what you mean. I disconnected the flex line that could fill the tank if the pump check valve failed and put it in a bucket. I ran the sink and the tub to see if it would fail and got not even a drip. Maybe one of the kids had turned the pump on when I got sprayed before. Those rascals cause more than a few minor accidents! I'll play with it some more when my wife is back and note the final verdict. Need to replace the city water anyway, so I'll do that, but it sounds like I need a pump as well.

[RustyJC]

atxshaws wrote:
You know the city water connection check valve sprayed me the other day when unhooking. Bet it is the cause.

If you were running the water pump, then the city water check valve might be bad and result in your getting sprayed. Failure of the city water check valve wouldn't fill the water tank, though - only the check valve in the water pump/fresh water tank line could cause that.

Rusty

[atxshaws]

You know the city water connection check valve sprayed me the other day when unhooking. Bet it is the cause. I had to replace the pump about a year ago. So I'm going for the city connection first which I have already bought a replacement for anyway. If it fills again tonight I guess I'll turn off the pump valve and go get a new pump. This forum is amazing! Thank you!

[atxshaws]

Thanks all! I'll start checking those check valves out!

[djousma]

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.

[RoyB]

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

[Greene728]

Yep. Bad check valve.

[The_Texan]

Been there done that, your check valve on the water pump has failed.

[Mile_High]

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.