Strange Part in a Strange Place

Phil, you can always install a back flow preventer in a more accessible location. I recommend a good brass one, like the one on my circa 1970's atwood.

http://www.ebay.ca/itm/RV-Plumbing-Back-Flow-Preventer-Brass-Check-Valve-Also-on-Water-Heaters-/161477596939?pt=Motors_RV_Trailer_Camper_Parts_Accessories&hash=item2598d0970b&vxp=mtr

Thanks again for all your help! These forums are an amazing source of help coming from a vast store of combined knowledge.

I'll have to decide whether to replace the valve or let it go. We don't winterize, and the valve requires some tricky hand and wrench angles to remove, so I'm leaning towards leaving it as is. If I do, I hope there's no other downsides to having no anti-syphon valve in the water heater outlet.

Water flow is 'out' of WH tank-----pressure pushes against back of plastic plunger disc (where stem is attached) opening disc against spring pressure.

No water flow------spring pressure pushes plastic plunger closed and o-ring seals. (Spring is compressed when disc is forced open)

Back flow is prevented because water pressure pushes against 'flat' head of plastic plunger disc which is being held closed via spring pressure and o-ring sealing.

The one in your city water inlet assemble works the same (same type---plastic plunger/spring/o-ring)
If you remove screen/washer you will see the 'tip' of plastic plunger.
Pushing it 'IN' opens it. (same as water does flowing 'out' of WH tank) Don't push on tip opening plunger with water pressure in system...it will dislodge o-ring and then you will have to repair/replace check valve)


As showing in this picture......water flow is from 'right to left'

Thanks for all of your great responses and invaluable information!

What I so far can't figure out is - when I looked directly into the tank's brass hot water outlet fitting's hole with the loose disc's stem facing into the tank and the flat disc part jammed in the fitting and facing outward towards me - which direction the anti-syphon action right there in that fitting was supposed to work?

i.e. To keep water from entering the tank there through the hot water outlet but being able to leave the tank through that fitting, it seems like the disc's stem with the spring around it should be facing outwards towards me so that the spring would be holding the o-ring against a rim in the brass fitting so that water could not come in through the outlet. However, the little white plastic piece was facing the other direction with only it's disc part facing me. :h

What they said. Check valve on water heater.

For what its worth your city water inlet also has one of these in it - Its a back flow preventer and both failed on my 2008 Winnebago- the hotwater one I replaced the city water I just reassembled.

Found the one in your picture after my winterizing took 2 gallons of water and was bleeding out the drain valve of the hotwater tank

It is the internals of the check valve on the hot outlet of your water heater.

A check valve is used vs a shutoff valve cause it's cheaper and easier to install.

The check valve is there so water does not back flow into water heater tank thru hot outlet when the water heater is bypassed (keeps from pumping anti-freeze into WH and allows water to flow thru hot lines when water heater is drained)

As you have found out..when they fail no hot water flows.

So you can:
Replace it (and wait for another failure of the cheap junk)
Install a shutoff valve in hot outlet line so you don't have check valve
Or just leave the internals out and forget about it unless you have to winterize RV using anti-freeze

Check valve came apart.

http://www.justanswer.com/rv-motorhome/6x5gm-suburban-sw6de-water-heater-storage.html

It could be an anti syphon valve from your shower faucets.

I wonder if it's part of the back flow preventer (or check valve)?