Hot Water Issue

[oldtrojan66]

Hey, Kids! There are a couple other posts nearby, that are close to my issue, but not close enough that I feel like hijacking their threads.

My issue, which I have had for some time is just wierd. Hers' what I know. When I turn on the heater in a full tank of water, it gets hot. Electric or propane, no matter. However, when I turn on the hot water, it is hot for only about 5-20 seconds, then goes to luke warm. Here's the fix. I must turn off the pump, open the drain plug, open the temp/press relief valve, and let about 2-3 gal run out on the ground. This is all hot water (the whole tank, actually, if I let it all out!). Put drain plug back in, close TPRV, turn pump back on and fill water tank by opening a hot water faucet. Turn heater back on, wait a bit and, voila! Hot water for shower, dishes, etc.

One other factor that may or not be relative. When the heater only produces 10 seconds of hot water, the pump will spontaneously run for about 1 sec, every couple hours, without running water. I have searched, diligently for any kind of leak, to no avail. Nothing, Nada, Zip! Everything I can see is dry! When the hot water continues to flow, this does not happen!

Here's what I'm thinking; There is supposed to be a bubble in the top of the heater tank, and when it's not there, the cold water mixes with the hot too quickly and turns luke warm. When the bubble is present, the mixing is correct.

Question; what happens to the bubble in the tank? Is it related to the pump running on it's own? Is there any other reason for the pump to run, other than a pressure drop? If not, why is there no water leaking when the system is under pressure all the time? What is there about this bubble, that I can't find any information about it anywhere?

I know someone out there in RV land will have the answer for my questions and I thank you sincerely in advance for the help!!! David

[RJsfishin]

Oh the horror stories that come from check valves and mixing valves in water heaters !!
The simple fact remains,...if cold water runs into a heater, and the fire is burning, hot water has no choice but to run out the HW faucet,....providing all the check valves, mixing valves, etc etc are removed ! MFGs are always trying stupid ideas that do nothing but cause many hours of grief later on down the line, and they couldn't care less,....maybe knowingly adding more business to the service departments ???

[dougrainer]

oldtrojan66 wrote:
Sorry to upset you, Doug. My Buddy does not need to be educated. He told me the very things you mention. There is debris in the valve causing it to mix too much cold water. Until I get this part cleaned properly, my wife and I are very capable of mixing our own cold water to avoid burns. As an added precaution, i have installed a lower temp thermostat in place of the relay that was there. I had 151.2 water, and now have 133 water by measurement. I am prepared for the lower volume of hot water this mod gives.

By the way, I'm sure, had I mentioned the model number many of you would have told me just what my Buddy told me only based on knowing the maker. At least the problem is now solved to my satisfaction. Thanks again, David

What I took issue with was in your post you stated that Atwood does NOT do that anymore. How would you know that if your buddy did not tell you? They DO install that Mixing valve on all EXT models. Doug

[oldtrojan66]

Sorry to upset you, Doug. My Buddy does not need to be educated. He told me the very things you mention. There is debris in the valve causing it to mix too much cold water. Until I get this part cleaned properly, my wife and I are very capable of mixing our own cold water to avoid burns. As an added precaution, i have installed a lower temp thermostat in place of the relay that was there. I had 151.2 water, and now have 133 water by measurement. I am prepared for the lower volume of hot water this mod gives.

By the way, I'm sure, had I mentioned the model number many of you would have told me just what my Buddy told me only based on knowing the maker. At least the problem is now solved to my satisfaction. Thanks again, David

[dougrainer]

oldtrojan66 wrote:
Ok, the fix is in! I talked to my buddy at Walnut Ridge RV service in New Castle, IN just a few miles from my home.

He had heard of this problem with some other units in the past. Turns out, Atwood is the only manufacturer who puts a "mixing valve" in the plumbing. They don't do it anymore, but the one I have, has this device. It is used to heat the water to a higher temp, then add cold as it is dispensed. Well, when it malfunctions, it just adds too much cold!

Now, you may disagree, but I have removed this device. I do not have one in my B & M home, and since other makers don't use it and Atwood doesn't either, I can add my own cold water to get the temp correct.

Thanks again, for all your ideas. Good ones, I agree, just something else this time. David

OK, you need to EDUCATE your buddy, because he does NOT know what he is doing or talking about. Atwood puts that mixing valve on because THAT XT model has 160 degree water instead of 130 degree water. The mixing valve takes the 160 water mixes it with incoming cold and then puts out 130 degree water. This allows your Hot Water to LAST longer. DO NOT REMOVE THAT VALVE. YOU WILL BURN YOURSELF OR ANYBODY ELSE. Why would you think because your B&M home does not have something, anything else does not need it either????????????????? Doug

[westend]

Valve cleaning: Buy liquid water softener cleaner (contains phosphoric acid). Immerse valve in cleaner for days. Rinse. Reinstall mixing valve.

[oldtrojan66]

Thanks to all for the words of wisdom. I will certainly check water temp at bathroom sink (hottest water there, it seems). We have no small children in RV and we will have to see how fast we run out of hot water. I have not changed anything that cannot be undone. Nothing was damaged. I did notice some debris in the (I believe) intake fitting of the valve. I would like to be able to figure out how to adequately clean out the valve.

[Old-Biscuit]

OK so you have an Atwood XT Model (that info would have been helpful earlier)

The Mixing valve allows higher temp setting (160*F normal t-stat) for heating cycle (vs 140*F on standard models) and then mixing cold water for an outlet temp of 130*F (6 gallon tank becomes a 9 gallon -----10 gallon becomes a 16 gallon equivalent for hot water availability)

The HOT out from tank (mixing valve in) gets clogged with scale/crud due to hard water/lack of flushing tank and then only cold water flows thru mixing valve supplying hot water system

Removing mixing valve.....huge liability
Immediate scalding if end user does NOT mix cold at faucet
Water will continue to be heated normal cycle to 160*F which will flow thru hot water system

IF you remove the mixing valve for safety replace the normal t-stat with the standard temp one (140*F)
The t-stats are same size......go in same place ...use the same ECO (high temp t-stat set to shutdown at 180*F)
BUT you will need to remove/replace the terminal spade on Brown Wire
Normal t-stat uses a smaller female spade.....the mixing valve version uses a round pin terminal

Be safe.....scalds are life changing and VERY PAINFUL


XT Models are still available

[DrewE]

westend wrote:
Be careful of scalding. I've forgotten what temperature the hot water is at with an Atwood with mixing valve but it is definitely hotter than the ones without. Your house water is not that hot.

The XT models maintain the tank temperature somewhere around 160 degrees. This temperature can cause 2nd and 3rd degree burns in half a second, according to the references I've been able to locate. If you want to get rid of the mixing valve, I would suggest also replacing the thermostat with a "normal" RV water heater thermostat (typically around 140 degrees) or lower if desired. It will mean you run out of hot water sooner when showering, but it might prevent some painful injuries.

Even ordinary RV water heaters are set to heat hotter than many domestic water heaters (140ish degrees vs 120ish degrees)

[Elk4me]

westend wrote:
Be careful of scalding. I've forgotten what temperature the hot water is at with an Atwood with mixing valve but it is definitely hotter than the ones without. Your house water is not that hot.

Ditto on this. I would use a meat thermometer and check the water temperature at a faucet. If it is above 120 degrees you are taking a chance of scalding if you have kiddos. I don't know if the thermostat is adjustable or not, some older ones were adjustable. Mixing valves are a pain. I'm a retired plumber, I know!

[westend]

Be careful of scalding. I've forgotten what temperature the hot water is at with an Atwood with mixing valve but it is definitely hotter than the ones without. Your house water is not that hot.

[oldtrojan66]

Ok, the fix is in! I talked to my buddy at Walnut Ridge RV service in New Castle, IN just a few miles from my home.

He had heard of this problem with some other units in the past. Turns out, Atwood is the only manufacturer who puts a "mixing valve" in the plumbing. They don't do it anymore, but the one I have, has this device. It is used to heat the water to a higher temp, then add cold as it is dispensed. Well, when it malfunctions, it just adds too much cold!

Now, you may disagree, but I have removed this device. I do not have one in my B & M home, and since other makers don't use it and Atwood doesn't either, I can add my own cold water to get the temp correct.

Thanks again, for all your ideas. Good ones, I agree, just something else this time. David

[rekoj71]

fpresto wrote:
If you have an outside shower make sure that the faucet handles are off not just the shower head. If open they allow the hot and cold to mix.

This was the cause when I had this problem. Kids used it and unly shut off the shower head. Almost took it to the dealer before I found it.

[westend]

oldtrojan66 wrote:
Thanks for the replies! I forgot to mention I have been around the check valve block several times. It is working as designed. I have removed the entire water heater when I thought I would need to replace it. When there was nothing wrong found, I replaced the unit, and checked the valve and the plumbing around the heater. I understand how the check valve works for winterizing and it is a normal in-line gate valve with one red handle to move the internal parts 90 degrees. All that is okay. I understand the check valve is the first place to look, and I have done that. I have also checked the outside shower (which has never been used) and it is turned off. I'm just saying, the only thing that gets me a full tank of useful hot water is to drain part of the water out, refill with the air space at the top and reheat. I just don't know why this is so. Thanks, again, david

A check valve is not a gate valve, it doesn't have a handle.

If you refill the heater with a faucet valve open, you are making any air bubble in the tank as small as possible, not adding any air.

I don't doubt that your procedure is getting you hot water, it is just the cause of the initial mixing that is at question.
Do you fill the water heater, initially, with a faucet valve open?

[Old-Biscuit]

Air pocket has NOTHING to do with you lack of HOT water FLOW

Water is being heated (electric/propane) and is available
Open a faucet and water pump runs causing hot water to flow out of water heater tank REGARDLESS f air pocket or no air pocket (air pocket is for control of pressure increase due to water swelling when heated---that is all it is for)

Water coming out hot then turning luke warm....
*COLD water has to be mixing with hot
**Cold water can mix with hot thru water heater bypass valve (open or leaking thru)
***Cold water can mix with hot thru inside/outside showers not being turned off using cold/hot knobs
*****Cold water can mix/dilute hot IF cold water inlet DIP tube has fallen off and cold water is no longer being directed DOWNWARD. (pointed down cold water creates a thermo barrier that pushes hotter water up/out.-----it not directed downward cold water can 'stream' upward and heavily cool the hot resulting in warm coming out)

This is an Atwood.........Suburban also uses 'dip tubes'
Need to look inside via drain hole or electric heat element opening etc and see if dip tubes are still in place