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Ask Dave: Why does RV water heater work on LP but not on 120 volt?

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusses an RV water heater.

Dear Dave,
I have a 2019 GD Imagine 2500RL which we bought in October 2020. The Atwood water heater only works on the gas mode. From what I have read and viewed online, it sounds as if my heating element has gone bad. How do you change the heating element?

Unfortunately, to get to the rear of the water heater, I have to work through the kitchen cabinet framework after drawers are removed. The dealer gave us spare fuses and they were installed, but there was no change. If the circuit board was bad, would gas also fail?  —Steve

Dear Steve,
It is either a 120-volt issue, ECO/Tstat, or a bad heating element. And, unfortunately, two of the three need to be diagnosed from the back of the water heater. It might be easier to remove the water heater and bench test, if possible.

This is the Atwood water heater I have in the shop that is for a Winnebago. It has the two “motor aid” connections on the side. The model is GCH10A-4E. The heating element goes in the large hole in the center and is covered by the black plastic box. To test the 120-volt operation, you will probably need to remove the box and have access to the heating element.

Checking the RV water heater element

Turn the 120-volt power off and remove the black plastic box to access the lugs of the heating element. Turn the power back on and verify the switch is in the on position. Next verify 120-volt power to the unit with a multimeter on the black and white wire coming from the romex wire. If there is no voltage, trace the wire back to the connection.

Turn the power off and check for continuity at the element, thermostat, and ECO switch. The thermostat and ECO switch are typically located on the front of the unit. The thermostat has a thermal cutoff fuse that you need to check first. Older models will have a reset button on the ECO.

Check continuity between the two pins of the thermostat and the ECO. If there is no continuity between either one, they need to be replaced.

Next, check continuity at the heating element probes. If there is none, replace the heating element.

One tip I got from my assistant, Steve Albright, at the RV Repair Club is to use a clamp-on amp meter at the distribution center to verify if the heating element is drawing amps. There will be a 20-amp circuit breaker in the distribution center specifically for the water heater. Identify the circuit breaker and the black wire coming out of it. Clamp the meter around the wire and set the dial to the amp setting.

This model is fairly inexpensive at Amazon.

Turn on the RV water heater on the 120-volt mode and it should register 11 amps. Make sure you have water in the tank or don’t let it run too long or it will ruin the element if it is good!

You can leave comments, however if you go to my new Forum, we can all share our experiences and see what the others have to say!

Read more from Dave here

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Jimmyb
9 days ago

FYI, 2021 Bighorn Traveler 39rk Factory wired the inside switch on control panel backwards, Dealer found this and advise me.

Joe
12 days ago

I often clean my water heater with the garden hose adapter. However, no matter how long and frequently I do this I get a lot of scale. I just got done installing a portable water softener with the hopes that it will help to reduce the scale. My question is… what are the thoughts of pumping several gallons of vinegar into the water system and heater and let it sit for several hours to a day to breakup most if not all of the scale? I have been doing that with our coffee maker for years without an issue.

Philip Racicot
13 days ago

DAVE LOOKING AT THE FRONT OF THE WATER HEATER YOU ARE TROUBLESHOOTING. THE CONTROLLER/IGNITION MODULE. IS 12V DC THE 4 AND 6 PIN CONNECTOR SHOWN TELLS ME THAT ( KNOWING THE WIRING DIAGRAM) FOR THAT MODEL ) ON THE 4 PIN CONNECTOR THE WHITE WIRE IS THE 12V SOURCE THAT ENERGISES THE 12V RELAY COIL THAT CLOSES THE CONTACTS FOR THE HEaTING ELEMENT TO WORK IT ALSO CLOSES AN INTERNAL RELAY IN THE IGNITION. MODULE TO ENABLE THE 12V relay to close for 120v element
To test RELAY without removing tank using a jumper wire between white wire on 4 pin connector to yellow wire on 6 pin connector
You should hear RELAY click in and if you have your Amp meter connected you you should see 11A as stated in your diagnostic
Testing. If you have 11A then element and RELAY are good
Then you can start to suspect that the internal relay in the IGNITION module is
Bad. As it was in my case

Crowman
13 days ago

Heating elements can last decades so my guess is he left the electric on when the tank was empty then plugged it in.

Bob p
13 days ago
Reply to  Crowman

Ditto