Hot Water Heater Boiling

[Regwal]

Recently when on a trip my hot water tank started to leak bad from the safety valve. I was on shore power at the time so I shut the power off and opened a hot water faucet to let cooler water into the heater. The heater seemed to have some air in it. After turning power back on the same thing happened after a while. I switched to gas and have not experienced the problem but once since and that was when I went back to shore power. Works fine on gas. When the safety valve was leaking and I opened a hot water valve steam came out. Any suggestions?

[jesilvas]

First, it was steam just due to the temp difference of the water and air, it wasn't boiling.

Second, without knowing model number, these are shots in the dark.

The control board relay might be sticking, the t-stat/eco asy. is bad, etc. etc. You will need a volt meter, or at least a test light, to trouble shoot to see where power is not being cut off at.

The WH is supposed to have air in it. So once you solve the issue, you drain all the water out that is above the pop off valve.

[ga traveler]

There are two thermostats on the heater. One is for gas and one for electric. It sounds like the electric thermostat is stuck or broken.

[dwhit]

I had this EXACT problem.

In my case the hot water electric thermostat assy (same as a residential water heater) had worked loose from its position from traveling...the double sided tape had weakened and the thermostat was no longer in direct contact with the tank which it MUST be to regulate temperature. She's all better now since I changed the tape and lowered the setting. My clear-coat was damaged below the overflow valve...polishing compound brought the finish back. The boiling water had turned my dark blue paint an unattractive white. No problems since the re-attachment.

[Regwal]

Thanks for everyone's input. Between rain showers today I'll have another look. I was looking for a screw in thermostat, did not know there are two.

[jesilvas]

Again, there may or may not be. Right now, without a model number, no one can tell you anything for sure.

[Gary RVRoamer]

Older Atwood water heaters had separate thermostats for AC and LP, but newer ones (last dozen years or so) have only one. Suburbans may be different than Atwoods too. We need the brand and model number to be sure, but the age of the RV might be enough to give a solid clue.

I doubt if the water was actually boiling - there are multiple safety interlocks to prevent that. For starters, you need to get the air out of the lines and re-establish the air head in the heater tank.

[deandec]

Open the pressure relief valve.

Caution, hot water!

Routine maintenance on water heater. It will be described in your manual.

[jesilvas]

Originally Posted by deandec

Open the pressure relief valve.

Caution, hot water!

Routine maintenance on water heater. It will be described in your manual.

That's only part of it. You open it when not under pressure or heating, to just exercise the valve. However, you then need to re-establish the air pocket in the top of the tank.

[Sky_Boss]

Originally Posted by ga traveler

There are two thermostats on the heater. One is for gas and one for electric. It sounds like the electric thermostat is stuck or broken.

I just found something very interesting along these lines. About 5 months ago I had my Suburban 12 gal WH with motor aid replaced. Recently it seemed that I couldn't get my gas function to fire up even though I could see the electric drawing current. It took a lot of cold water through the WH to get the gas function to work even though the electric element was running.

At the recent Newmar rally we only had 30 amp service so wanted to switch to gas but we couldn't seem to get the WH to fire up. To be most correct, I could see the WH using 10 amps but the gas side wouldn't fire up. I thought the gas feature was totally inop so I asked one of the techs to take a look at it. The tech came over and after nearly 3 minutes of running hot water it fires up. That seemed like a long time so the tech told me he would bring over their HWH guru to look at it.

When the guru came over I explained what was happening. He removed the rubber cover of the reset switches that also includes the thermostats and he immediately saw the problem At the factory they let a wire to the gas thermostat slip behind the plate holding the electric thermostat so that it didn't have solid contact with the water tank. That meant that the water temp needed to get much hotter than 120* to satisfy that thermostat. That explains why we typically saw 125-130* out of the faucet. Of course, that meant the 120* gas thermostat was always satisfied and never needed to run unless we had the system turned off for along time or a lot of water had gone through the WH. He moved the wire out of the way, straightened the plate out and put it back together. So far we haven't seen the problem with the gas anymore and our water temps seemed much more with 120* in both electric or gas only modes.

No wonder the water seemed too hot for us. It might also explain the electric bills we got that we thought seemed a tad high in KW Hours used.

BTW...I didn't know it had 2 thermostats until I saw the set up when the tech worked on it. I now know better.

[Sky_Boss]

Originally Posted by Gary RVRoamer

...For starters, you need to get the air out of the lines and re-establish the air head in the heater tank.

Feeling stupid but...how do you re-establish the air head?

[Fred Cooper]

Originally Posted by Sky_Boss

Feeling stupid but...how do you re-establish the air head?

I always drain the water heater after every trip, and the air head gets re-established without a problem. I had to look up the correct procedure.

The instructions below were copied from the Atwood manual.

Weeping or dripping of a pressure-temperature relief valve while the water heater is running DOES NOT mean it is defective. This is normal expansion of water as it is heated in the closed water system of a recreation vehicle. The Atwood water heater tank is designed with an internal air gap at the top of the tank to reduce the possibility of weeping and dripping. In time, the expanding water will absorb this air. To replace the air follow these steps: Step 1: Turn off water heater Step 2: Turn off incoming water supply Step 3: Open the closest hot water faucet in the coach Step 4: Pull handle of pressure-temperature relief valve straight out and allow water to flow until it stops. Step 5: Allow pressure-temperature relief valve to snap shut, turn on water supply and close faucet.

Fred

[Regwal]

Yesterday I got back to my water heater problem and here is what was found. There is a thermostat stuck to the tank, on the backside that had fallen off. I removed the access panel from inside closet and saw thermostat just laying on floor. After scratching my head for a bit trying to figure out how this worked I gave up and called Atwood. The rep told me someone had converted this heater to a gas/ electric unit. According to my ser# mine was originally gas only. Is this safe? Has anyone done this? It was working fine until the thermostat detached from the tank.

[jesilvas]

Again, what is the model number?