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Old 08-15-2022, 06:48 PM   #1
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water heater issue

I have an Atwood/Dometic water heater in my 04 Allegro motorhome. It was originally set up as gas only but at some point, the previous owner had an electric element installed. The heater no longer works on electric but is fine on propane. I removed and replaced the electric element, tested to make sure it has 120V in and also removed and checked the cutoff relay on the back side of the element that controls the water temperature. At this point I have to think that there is no power going into the relay coil to make the 120V connection to the element. I don't really know how to trouble shoot it any further, and am afraid of digging in too deep for fear of screwing up the propane side of it. I'm at a seasonal site with shore power and it would be nice not to have to use up all my propane when I could be using their electricity.
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Old 08-15-2022, 07:02 PM   #2
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Model of this unique gas only converted electric water heater???

6 gal 8E/9E or 10 gal 3E versions have separate controls for gas and electric
Electric has its own set of t-stats for temp control on backside along with the element (and the OEM On/Off Switch)
*120VAC from 15A CB to high temp t-stat to t-stat to element (black wires) then back to AC power panel on White wire (neutral)
High temp t-stat has manual reset.....which means t-stat failed

If 6 gal GC6AA-10E or 10 gal GC10A-4E models (new version in 2004)
Both gas/electric use DC for controls. one set of t-stats
Electric uses a DC Relay on backside of tank to trigger the 120VAC to element
*DC from circuit board to DC relay via YELLOW wire
Bad DC Relay...no 120VAC to element

So MODEL number (on label in outside compartment) is helpful


And if GAS only converted to AC Element...then aftermarket element installed in the drain plug with its own set of T-stats which should have a resettable High temp t-stat
*Nothing to do with function/operation of GAS


Side Note: Owners Manual for Allegro Bus shows 10 Gal Gas/Electric Combo Water Heater (GC10A-4E)
So it would use a DC Relay

https://tiffinmotorhomes-rcgarkskyk9...llegro-Bus.pdf
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Old 08-16-2022, 07:10 AM   #3
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Quote:
Originally Posted by Old-Biscuit View Post
Model of this unique gas only converted electric water heater???

6 gal 8E/9E or 10 gal 3E versions have separate controls for gas and electric
Electric has its own set of t-stats for temp control on backside along with the element (and the OEM On/Off Switch)
*120VAC from 15A CB to high temp t-stat to t-stat to element (black wires) then back to AC power panel on White wire (neutral)
High temp t-stat has manual reset.....which means t-stat failed

If 6 gal GC6AA-10E or 10 gal GC10A-4E models (new version in 2004)
Both gas/electric use DC for controls. one set of t-stats
Electric uses a DC Relay on backside of tank to trigger the 120VAC to element
*DC from circuit board to DC relay via YELLOW wire
Bad DC Relay...no 120VAC to element

So MODEL number (on label in outside compartment) is helpful


And if GAS only converted to AC Element...then aftermarket element installed in the drain plug with its own set of T-stats which should have a resettable High temp t-stat
*Nothing to do with function/operation of GAS


Side Note: Owners Manual for Allegro Bus shows 10 Gal Gas/Electric Combo Water Heater (GC10A-4E)
So it would use a DC Relay

https://tiffinmotorhomes-rcgarkskyk9...llegro-Bus.pdf
It is a 6 gallon heater. The element is in the back of the heater with the relay in the same spot. I know it was added later because there is a switch panel for either gas or electric operation and there was never a switch in the panel for electric. The only way to turn it on or off was by plugging or unplugging it from an outlet located next to the bypass valves. No switch to be found anywhere, and I looked for it hard. I know the relay works. Took it out and triggered it with a 6 volt motorcycle battery and it completed the circuit that runs to the element . I watched a few You Tube videos and they mentioned a thermo couple that might have failed. I won't know till I get back to it Friday if thats the problem, or if it even has one.
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Old 08-16-2022, 10:29 AM   #4
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Should be a YELLOW wire going to that DC Relay with BLACK AC wires to/from relay

YELLOW gets 12VDC from circuit board (in outside compartment)
No DC on Yellow when Electric Switch is ON then Relay can not close to allow 120VAC to element

No DC on Yellow.........circuit board faulty

Thermocouple...........NONE used
Thermal Fuse (device in clear tubing with Brown wires connected in each end. Blows when exposed to 190*F from flame blow back
But if Blown...no DC back to circuit board....No Gas or Electric Operation

Element would have always been there otherwise there would have been a large open hole in tank.
Switch might have been overlooked, forgotten etc.

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Old 08-16-2022, 11:56 AM   #5
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Thank You very much for the wiring diagram. Two more questions then and I'll leave you alone. I should have continuity across the thermal cutoff and fixed temp thermostat on the brown wire? And if I follow the white wire out of the circuit board I should find or be able to install a switch and pilot light to run the electric side?...OK, maybe 3 questions...or 4. Did they ever wire both sides, gas and electric, to come on off of the same switch with the electric side set at a lower cutoff temp for maintaining temp with the gas off? And if I wanted to run them independent of each other all I need do is put a switch in either the green or yellow lead off of the relay?
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Old 08-16-2022, 12:15 PM   #6
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OK-after studying the diagram a bit more I see that if either of the thermal controls are bad neither side of the heater would work, and likewise with the white wire, no power no gas operation either.
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Old 08-16-2022, 01:05 PM   #7
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My Mom bought an old 1980 something trailer a while back. It had a switch in the kitchen that fired up the propane. Because there was only the one switch, I assumed there was no electric element in the tank. She ended up having a slight leak that looked to be coming from under where the water heater sat so I looked under the bed to see about making the repair.

The repair turned out to be easy with a tightening of a fitting. Even better, I noticed the tank had an element along with some controls. That control had its own switch. Turned it on and I don't think she ever used propane again. Don't remember if it was an Atwood or Suburban.

Moral of the story, the switch was on the control box, on the backside of the tank, completely out of sight.
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Old 08-16-2022, 01:42 PM   #8
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Common 12VDC from a fused source would feed both switches for power
Gas Switch sends 12VDC to circuit board via ORANGE wire
Electric Switch sends 12VDC to circuit board via WHITE wire

Then Circuit board sends 12VDC to T-stat via Brown wire which then goes back to circuit board thru Thermal Fuse via Brown wire

Then 12VDC to/thru ECO to gas valve for GAS operation
OR
Millivolt DC to/thru ECO to gas valve AND 12VDC to DC Relay via YELLOW wire for Electric operation
*Millivolt is used so ECO is part of temp safety control loop circuit

Both gas & Electric can be used at same time by turning both switches on....T-stat opens at 140*F and shuts down Gas, Electric or Both
**One switch could be used....white/orange wires together but Gas and Electric would ALWAYS come on together

Dual Switch
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Old 08-16-2022, 01:45 PM   #9
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Quote:
Originally Posted by Mudfrog View Post
My Mom bought an old 1980 something trailer a while back. It had a switch in the kitchen that fired up the propane. Because there was only the one switch, I assumed there was no electric element in the tank. She ended up having a slight leak that looked to be coming from under where the water heater sat so I looked under the bed to see about making the repair.

The repair turned out to be easy with a tightening of a fitting. Even better, I noticed the tank had an element along with some controls. That control had its own switch. Turned it on and I don't think she ever used propane again. Don't remember if it was an Atwood or Suburban.

Moral of the story, the switch was on the control box, on the backside of the tank, completely out of sight.
Atwood used separate controls for gas & electric on various models up thru 2003
Electric OEM on/off switch was on cover over element and set of AC t-stats

2004 new design...dual switch/DC controls/one set of T-stats
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Old 08-16-2022, 02:11 PM   #10
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Originally Posted by Old-Biscuit View Post

Both gas & Electric can be used at same time by turning both switches on....T-stat opens at 140*F and shuts down Gas, Electric or Both
**One switch could be used....white/orange wires together but Gas and Electric would ALWAYS come on together

Dual Switch
This is what has me confused. There is no switch anywhere for the electric. My switch plate looks like your illustration but the electric side is blanked off and thats what led me to think electric element was added later. If I pull the panel off and find two dead headed wires I will be amazed (amused?) that somebody would go through all that trouble and NOT take the final INEXPENSIVE step of hooking it up.
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Old 08-16-2022, 02:15 PM   #11
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Switch for electric may have failed....previous owner just blanked it off vs finding/installing a new switch


??????


If you have the DUAL switch, then I would bet dollars to donuts the wiring for second (electric) switch is present
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Old 08-16-2022, 02:29 PM   #12
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Won't know till I go back over to the camp ground Friday but the suspense is killing me. Hope it doesn't keep me awake at night.

Thanks again for your help
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Old 08-16-2022, 06:49 PM   #13
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Seeing as how the Atwood Combo water heater was Standard Equipment, I would imagine inside the AC Power Panel is a 15A Circuit Breaker for WH Element that powers that outlet it is plugged into.
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Old 08-16-2022, 08:22 PM   #14
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Seeing as how the Atwood Combo water heater was Standard Equipment, I would imagine inside the AC Power Panel is a 15A Circuit Breaker for WH Element that powers that outlet it is plugged into.
Well now thats another mystery. There is no dedicated breaker in the AC panel for the water heater. The outlet for it is wired in with another outlet that was added into an outside compartment for a TV. It is powered by a tandem 20 amp breaker, the other half of which powers various other outlets in the rig.
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