Atwood WH Thermal Cut Off Switch

[j griff]

I know this is an old subject, but have not been able to bring up some of the posts I think I remember. Troth was most helpful in replying to an email with pictures of his modification to allow access to the rear of the water heater.
I may have left the w heater on momentarily when I winterized last November, so it is quite possible that I fried the element. Tom Roth advises that it may be just a thermal cut off switch so that is what I am looking for.
I am able to get the bottom of the black plastic cover up a little ways and can see what is under it (wiring to elec element, etc.,) but I do not find a circuit breaker/thermal cut off switch. Tom describes it as a little black switch that one depresses. I have been unable to get the cover all the way off as I can not unscrew the top nut holding it in place with my fingers and there is so little room to attempt to get a rachet/socket on it. I would certainly like to solve this problem without removing the entire wh.
Anyway, any further help will be appreciated.

[JohnFitz]

Short answer: I think the reset button is only on older WH units. New units use the LP circuitry safety devices- so if it runs OK on LP but not electric it probably a burned out element.

Long answer:
I replaced my 1991 Atwood WH in 2006 with a new unit and noticed they had changed the heating element control method. The old unit had a thermostat/safety breaker (with a button for resetting) right next to the element- all on the backside of the WH. They were just like the ones used on a residential electric WH. I had a 120volt wall switch by the bed that was used to turn it on and off.

The new unit had only a relay next to the element on the back. The new control method uses the LP thermostat, safety cut-off and circuit board to provide a 12 signal to the relay in the back. To turn it on and off you use a 12 volt switch to send a signal to the circuit board.

I know what a pain it is to pull-out the WH if there's no easy rear access. To make things easier for me I added braded flex hoses (like those used on toilets and facets) between the connections so I can make all connections with the WH face down on a small table at the compartment height. This way I could verify there were no leaks and also not have to bust my knuckles reaching behind the WH.

When I winterize I pull the connectors on the WH circuit board just to prevent such a problem.

Hope this helps.

[PanJH]

The thermostat and ECO are mine are on the front of the unit. When you open the outside access door, they will be on under a cardboard type of cover with a few wires attached. The thermo and ECO are two disk type devices that slip/twist in and are held with springs. They come as a kit for under $20. There is no reset button on mine either

[Roadking]

On most older (prior to 2008) Attwood 6 gal and 10gal HWH's the LP gas Tstat and ECO devices are located on the front and the 120VAC Tstat and ECO are located on the back. The ECO and Tstat are a bi-metalic disk switch.es. Being a switch each devices has two wire spade lug type connectors that plug in.

The 120VAC ECO and TSTAT look very similar to the LP ones located on the front. The 120VAC ECO is manually resettable whereas the LP ECO will automattically reset.

On the 120VAC ECO the reset button is located directly between the two wires. If the 120VAC ECO tripped it can be reset by simply pushing in the small round button located directly between the two wires. Caution... those two wires are 120VAC so it is recommended the HWH AC switch or circuit breaker be turned off prior to putting your fingers or any metal devices on the switch. The ECO is a "disc" switch, so the button barely moves and will "click" when reset. It should take very, very, very little effort to push the botton.

The ECO stands for "Emergency Cut Off". So the real question is why did the ECO trip??? A common failure mode is the Tstat fails to open and the HWH overheats thus causing the ECO to trip. Most RV centers and stores carry these switches and they are sold as the pair (Tstat and ECO) and cost about $25 to $30. IF either has failed, replace as a pair.

[DAN L]

Originally Posted by Roadking

On most older (prior to 2008) Attwood 6 gal and 10gal HWH's the LP gas Tstat and ECO devices are located on the front and the 120VAC Tstat and ECO are located on the back. The ECO and Tstat are a bi-metalic disk switch.es. Being a switch each devices has two wire spade lug type connectors that plug in.

The 120VAC ECO and TSTAT look very similar to the LP ones located on the front. The 120VAC ECO is manually resettable whereas the LP ECO will automattically reset.

On the 120VAC ECO the reset button is located directly between the two wires. If the 120VAC ECO tripped it can be reset by simply pushing in the small round button located directly between the two wires. Caution... those two wires are 120VAC so it is recommended the HWH AC switch or circuit breaker be turned off prior to putting your fingers or any metal devices on the switch. The ECO is a "disc" switch, so the button barely moves and will "click" when reset. It should take very, very, very little effort to push the botton.

The ECO stands for "Emergency Cut Off". So the real question is why did the ECO trip??? A common failure mode is the Tstat fails to open and the HWH overheats thus causing the ECO to trip. Most RV centers and stores carry these switches and they are sold as the pair (Tstat and ECO) and cost about $25 to $30. IF either has failed, replace as a pair.

if you have the winnebago "motor aid" water heater in your moho, be sure to turn off the ac water heater switch before plugging into shore power. the engine coolant runs at 195 degrees+ and the motor aid heat exchanger will heat the water in the water heater to that temperature while you are driving. if you plug in shore power with the ac water heater switch turned on, the water in the heater will be hot enough to trip the eco switch.
you need to use a lot of hot water before turning on the ac switch.
part of my before driving checklist is turning off the ac and propane water heater switches.

[Roadking]

Dan L -- You make an excellent point about the Motoraid with coolant temps of 195-205F. Clearly the heat sources from AC heater and the propane flame temps are in the very high hundreds of degrees and these sources are turned off once the water reaches the Tstat temp. If the water in the HWH is ambient temp I know the heating time from either AC or propane is not that long.... maybe 30-45 minutes max. When the water is already warm, say 130-140 degrees, the propane or AC heat source would only be on a few minutes, say maybe 5-10 minutes.

With 195-205 degree coolent temp the rate of heat transfer from the motoraid to the HWH tank is clearly time dependent and heating the HWH tank would take much longer than the propane or AC heater sources.

So assume you're parked and the water heater is warm, or already up to temp (130-140 degrees F) and further assume your engine temp is cold. A typical routine would be to unplug, pack up, start the engine, and head down the road. The hotwater would begin to cool some, but I have no clue how much. Clearly if one drove forever... at some point, or time, the HWH temp would equal the coolant temp. So the interesting question is, how many hours of driving time it would take for the water temp to exceed the ECO temp?

I know the Motoraid is simply a length of aluminum pipe welded to the rear bottom of the HWH tank. The Motoraid pipe is about 1/2 inch diameter and about 12 inches long. While driving I don't know what the coolant flow rate would be, nor do I know what the actual coolant temp at the motoraid would be. Also there are heat losses in the hot water tank and I have no clue what these would be and these losses are dependent upon air flows and external temps.. Pretty complicated thermodynamical mathematics...similar to analyzing components and systems used in a space shuttle rocket launch. So my thermodynamics knowledge is absolutely zero, but I bet someone could calculate transfer rates and estimate how long it would take to heat 6 or 10 gallons of water. or better yet, practical knowledge as perchance someone has actual measurements?

When I'm traveling I usually average about 250 - 300 miles which would be about 5 or 6 hours of driving. Given the above assumptions would, or could, the water temp actually exceed the ECO temp in this driving period? Like I said, after driving and once parked I know the water is warm, but is it actually hotter than what the propane or AC would produce? If I remember it, the next time I hit the road I'll collect some measurements.