Holding tank water backflowing.

[Stump Jumper]

Filled up the holding tank for the first time this year. Noticed that when I pump the hot water tank full of holding tank water, I start to get water coming out the connection where the city water connects to the motorhome. I assume there is some type of backflow preventer valve that is probably stuck and allowing this to happen. Any ideas or opinions?

[bdpreece]

You may have more than one failed component in the system. Most coaches will have at least one check valve on the hot water heater and another check valve on the city water connection.

[Stump Jumper]

Would the check valve be located close to the hot water tank and/or city water connection?

[bdpreece]

I would start with the one behind the fresh water connection. They are usually spring loaded and sometimes can just be repaired by sticking a coat hanger in the inlet and snapping it a couple of times to get it to reset. You will probably have to remove the screen filter at the inlet first. The back flow preventer will look something like this Camco 1/2" Back Flow Preventer - Hose Accessories - Fresh Water Connection - Plumbing
on the back side of your water inlet.

[Mike Canter]

Brian is 100% correct. Usually they are gray plastic (cheap) see here
Pump Fittings :: RV Fresh Water :: RV Parts Store

Mine is located between my hose reel and thye MH pipe to the water tank switch valve.

[LVJ58]

Had a similar problem, so installed one of these:

Gilmour 03V Garden Hose Brass Shutoff

[Mike Canter]

Jim, that was exactly waht I did until I found out what the problem was. the check valve is only $6.95 and then all works normal.