Hot water problem

[navy flier]

I posted this on RV.Net but thought that I would expand my audience. On my 2008 Horizon I have an Atwood 10 gal gas/elec water heater that no longer provides hot water. I flushed the tank and the water that came out was too hot to touch. Therefore, the water in the tank is hot but I am getting cold water at the faucets. Initially, I was using the elec side and the water turned cold so I switched to the gas side thinking that the elec element had gone bad. I got sort of hot water but not as hot as it should be. Now even that has gone away. I do have good flow pressure from all of the hot water faucets and the shower.  The bypass valve is set correctly as is the outside shower. Have I got a one way valve that is inop or is there an air block? Little tough to evaluate since the tank is not easily observable.

 

[Alfa38User]

One of 2 things, the check valve in the tank output hot side has failed (top connection). You can remove it or its guts temporarily or simply replace it with a new one available in most hardware stores. Watch the arrow is pointing correctly if replacing!!! It is needed only if winterizing and prevents dumping a lot of antifreeze  into the tank at that time.

Other than that you could have a shower valve shutting off the water at the shower head instead of the main faucet. This can cause mixing hot and cold and can be located inside at the shower head or at the outside shower head, if equipped.

 

[Rene T]

One of 2 things, the check valve in the tank output hot side has failed (top connection). You can remove it or its guts temporarily or simply replace it with a new one available in most hardware stores. Watch the arrow is pointing correctly if replacing!!!

Other than that you could have a shower valve shutting off the water at the shower head. This can cause mixing hot and cold and can be located inside at the shower head or at the outside shower head, if equipped.

Stu, the OP said that they are getting good flow at all the faucets so I think that rules out the check valve and also said that the outside shower valves are position correctly. All I can think is the inside shower. Those valves have to be checked to make sure they are shut and not just at the shower head.  The only other thing it may be is the bypass valves are not positioned correctly.
For the OP, was the heater working OK at one time and then just all of a sudden stopped working without doing anything to the bypass system?

 

[Becks]

Had the same thing with a past Winnebago, and it was the check valve.

 

[Rene T]

Had the same thing with a past Winnebago, and it was the check valve.

Usually when the check valve fails, the water flow is drastically reduced because the failed parts obstruct the water flow.  I could be wrong.  If water was still able to flow through a bad check valve, it should still be hot at the faucet but the volume would be reduced.  I believe somehow there is cold water transferring over to the hot side cooling the water down. That's only my opinion.

 

[John Canfield]

Another vote for a bad check valve, there are two of them used on the hot water heater and their failure rate is rather high.

 

[Clay L]

My winterizing diverter valve developed a very small leak from the cold water line to the hot water line and that reduced the temperature of the water from the heater to pretty much cold water. I replaced the valve and fixed the problem. What was surprising was that a leak that small could drop the temp so much.
I say it was small because when I blew into to it not much air crossed over. I guess under pressure quite a bit of water could have crossed over

 

[Steve COH]

Another vote for a bad check valve.  Had exactly the same thing happen and it was a check valve.  Change the check valve.

 

[Bob T]

My money is on check valve.
Had this happen last spring. Ended up taking apart and removing checkvalve, mixing part of valve no longer worked and water VERY HOT but it got us through season.
New one in toolbox to put in while south in April.

 

[Dan T]

Where is the check valve?

I am having a similar problem right now.  The water heater itself is working and heating the water in the recently replaced tank.  We aren't getting any water moving through the hot water line.  Occasionally we get dribbles that quickly stop.  This fits the check valve descriptions listed above.

I have a 2011 Adventurer.  I am familiar with the two under bay valves, one for the winterizing tank bypass and the other for drawing antifreeze into the waterlines.  I'm also familiar with the pressure relief valve on the tank.  None of these would seem to be the check valve. 

I can turn the bypass valve to bypass and it will pass cold water through the hot water lines.  When I turn it the other direction it shuts down the hot water side completely.  It doesn't point directly at the Normal Operation mark. It comes up short. 

 

[John Canfield]

There's two of them on the rear of the water heater in a difficult place to access.

 

[RVfixer]

Hey guys, I'm not getting this...I have seen plenty of blocked check valves but they result in low flow at hot faucets.  How does a blocked check valve change the temperature of the water flowing through the hot water line?  If you block the cold water entering the water heater you get low flow at the hot faucets.  If you block the water exiting the water heater you get low flow at the hot faucets...how does a bad check valve change to colder water at the hot faucets?  The op said he has good flow at all the hot faucets but the water is cold there... but hot in the water heater.  How can that be with bypass valves correct and water off at shower faucets?  Sounds like the water is bypassing to me.

 

[Bob T]

These are photos I took last season of the mixing/check valve.
It's located on the back side of the hot water tank. It's the large chrome part.
You will see a grey valve, that is not part of original installation. I had to raid the boat parts that I've saved over the years. That was to limit the amount of cold water that was put into valve once I stripped out interrior parts.
I replaced it when I arrived in Myrtle Beach 10 days ago and it now works perfectly.
If needed I can take photos of the papers that came with the new one and post.
Let me know if those photos would be of any benefit to you.
Bob

Sent from my iPhone

 

[Clay L]

Hey guys, I'm not getting this...I have seen plenty of blocked check valves but they result in low flow at hot faucets.  How does a blocked check valve change the temperature of the water flowing through the hot water line?  If you block the cold water entering the water heater you get low flow at the hot faucets.  If you block the water exiting the water heater you get low flow at the hot faucets...how does a bad check valve change to colder water at the hot faucets?  The op said he has good flow at all the hot faucets but the water is cold there... but hot in the water heater.  How can that be with bypass valves correct and water off at shower faucets?  Sounds like the water is bypassing to me.

I agree.

 

[Dan T]

I get cold water through the hot water lines with the hot water tank bypass valve on.  The purpose of the valve is to avoid filling the tank with antifreeze.  When I checked with a local shop he said that's exactly what should happen if I have the bypass valve on.  I presume the bypass cold water simply rejoins the hot water line downstream of the bypassed hot water tank.

From all of your descriptions and the fact that I've eliminated everything else that I can think of I'm pretty sure you guys have nailed the problem.   

I found the check valve right where John said it would be.  It is hard to reach.  I think I'm going to have the shop do it.

Thanks everybody 

 

[Dan T]

I misunderstood Clay's "i don't get it" point.  I deliberately turned the bypass on in order to see if there was a line blockage somewhere.  The cold water ran properly through the hot water lines.  The only time I had any evidence of blockage was when the valve was set on normal and should have been passing hot water.  Then little to no water passed through the hot water lines.

Dan

 

[Dan T]

I'm 90% convinced that my problem is with a check valve.  The symptoms exactly meet your descriptions.  Little or no water at all through the hot water lines when the bypass valve is properly set.  Actually when the faucets have been off for a while the lines will typically pass a little hot water when first turned on, then reduce to a dribble then shut down virtually none at all.

The RV mechanic I spoke to on the phone said I could check to see if it was the valve by removing the hot water drain plug, opening the pressure relief valve, hooking up to city water then turning it all on.  If the water flows through the hot water tank the check valve is working.

His description makes sense to me.  At least if there is only one check valve and it's on the input side of the hot water tank.  If there is a second valve on the output side of the tank, that could be faulty and the water would still flow out of the drain on the tank. 

Some of your posts have mentioned two valves.  I have a ten gallon Atwood that replaced a six gallon tank that I broke with I didn't pull the drain plug the winter before last.    Are there two valves and if so which one would be the most likely culprit?  I found one near the top of the tank and didn't look for a second one which I presume would be near the bottom.

I've decided to crawl under the motorhome and do the work myself if I can be fairly confident I know what the problem is.

Thanks again everybody,
Dan T

 

[8Muddypaws]

Depends on where the check valve is. 

I just replaced my mixing valve a few weeks ago and my check valves were both installed where the flexible lines were attached to the hard lines.  If it were a check valve (with the same configuration you'd not get any flow.  Some of the older mixing valves have a built in check valve.  Mine did but the new one doesn't.  Same result though.

I can't imaging any configuration that would put the check valve anywhere but on the input side before the mixing valve and cold water path, so my vote goes for a completely blocked mixing valve.

If you can get the mixing valve off without removing the water heater you may want to temporarily allow about a gallon of water to flow through and out the upper port to flush out any 'chunks' that might be in the curved internal tube.  (If you look at a picture of the tank internals this will all make sense)

Replace the mixing valve (about $130 on Amazon) or try letting it soak in white vinegar for a couple of days.

If you have to take the tank out to get at the valve take the opportunity to completly flush it out by Putting a gallon or so in it, shaking it, and tipping it forward.  I got a ton of chunks out of mine.  Enough that the wife wanted to what I'd done to her driveway.

 

[Alfa38User]

The check valves I have encountered on my Suburban tank are simply screwed into the tank input pipe threads (bottom - cold) and the tank output pipe threads (top-hot). From there the plastic (PEX) plumbing is connected directly to the check valve input or output (as the case may be) using any adapters required. There are no mixing valves on mine (AFIK!!).

(Note: the valves are not identical, they are directional so each has a different part number when shopping for replacements!!) They can be purchased at any large plumbing shop or big box store as they are not special to RV's.

In Dan T's case the hot side(top) would be my primary suspect (he may have only a hot side one way valve!!) otherwise if a cold water valve was problematic, then the tank would not fill well. Be sure to turn the electric element off, stop the tank from gas heating and remove the water supply while working there. You will likely have to drain the tank down a bit to prevent a flood.

 

[Rene T]

Never heard back from the original OP as to whether their problem is fixed. I wish everyone would just reply as to whether we were able to help them.