Dometic wter heater lit itself with switch off

[wdonovan]

Last night while outside cooking, wife was inside and was running water f.o.r.e.v.e.r.
Then I hear a gas fire and see the water heater is running. I get confused and go inside.
Checked the switches and "gas" was off, "electric" was on. What would make the gas
light? She had literally used up every drop of hot water. Is there a thermal switch that
automatically starts a gas flame at a preset temperature below the heaters thermostat?
Does the electronic control module control both gas and electric? Is this the most likely suspect?
Confused.

[Second Chance]

As far as I know, there is nothing that would turn the gas on when the "Gas" control switch is off. The first thing I would check would be to see if the wires on the two switches are reversed. Turn the "Electric" switch off, too, and run enough hot water for the temp to drop - then see if the gas cycles on.

Rob

[wdonovan]

Thanks. After a lot of thought, I think the problem has to be voltage at the output side of the "gas" switch. That's the only thing that makes sense. Atwood service manual says both gas and electric can run at the same time as they have separate thermostats.

[Second Chance]

Thanks. After a lot of thought, I think the problem has to be voltage at the output side of the "gas" switch.

That doesn't make sense unless the switch has failed internally. The best way to find out is to remove the panel, tilt it out, and use a multimeter to see if there is voltage from the control side of the switch to ground when the switch is off.

Rob

[wdonovan]

It can make sense if wiring past the switch is incorrect. Some time back I wired a dimmer on the house ceiling light circuit. It needed power to the electronics and I need to check if that mod wound up feeding the gas switch output. I seriously doubt it but something fed power to the downside wiring.

With the two heating options and separate thermostats it may be possible that during normal use only the electric thermo usually trips but when my wife ran the tank cold, the gas gor a signal from the thermo and fired up. I will have to pull the panel and check for downstream voltage.

[Second Chance]

It can make sense if wiring past the switch is incorrect. Some time back I wired a dimmer on the house ceiling light circuit. It needed power to the electronics and I need to check if that mod wound up feeding the gas switch output. I seriously doubt it but something fed power to the downside wiring.

With the two heating options and separate thermostats it may be possible that during normal use only the electric thermo usually trips but when my wife ran the tank cold, the gas gor a signal from the thermo and fired up. I will have to pull the panel and check for downstream voltage.

We have run the WH until cold in both our rigs while on electric-only... the gas never switched on.

Rob

[FT4NOW]

I dont think your thermostat theory is the answer. It's more likely that something is miswired one way or the other (on the interior control panel or any mods you might have done). Are you 100% certain it hasnt always been like this? Sounds like you just happened to be in the right spot when the burner fired up.

If it were me, I'd start by checking that the switch isnt dead/faulty, and then checking the output side of the switch for voltage while the switch is in the off position.

I dont know how you wired the dimmer or which one you have, but if you tapped into another circuit besides the light circuit for some reason, it's worth checking that as well.

[wdonovan]

Looks like I'm confusing people with my wording. I do not think the dual thermo setup is the problem. I just think it is what ultimately showed me there was a problem.

I think the most likely reason for gas firing up is, one way or the other, the output of the gas switch must be energized. Either because of internal switch failure (though it feels fine) or incorrect wiring which essentially bypasses the switch (although the internal switch light is not on). In my mind I cannot see how the solenoid and controller can energize without voltage.

As far as the dual thermo, my theory is that:
1) This issue of a hot circuit has been around for some time. It has not just happened.
2) It never acted up before because during normal use, whenever the electric heater thermo saw low temp it cycled the electric heater.
3) The gas thermo is set for a lower temp than the elec thermo.
4) The one time the gas kicked on is when my wife turned on the galley faucet and ignored it. That lowered the temp enough for the elec heater to start (separate thermostat).
5) The electric heater could not keep up and the water temp dropped further until the gas thermo was stepped on, lighting the gas heater. And the gas heater started because the circuit was somehow energized.

When I installed the dimmer, it was a solid state unit that needed 3 wires - hot, lights, ground. The main panel in the trailer has only one access to ground wires which was the neg side of the indicator lights on a few toggle switches. Two of them were the electric heater and gas heater and they were tied together. I tapped my ground wire from the dimmer into this connection. I just sketched the wiring (as I intended... not confirmed) and I can't see a way for voltage to backfeed the gas circuit. Also, if the gas circuit was corrupted then the electric circuit should be as well.

As I type this I am talking myself out of the possibly of the switch output being backfed. The "elec" indicator light is on with that switch on and the "gas" light is off with the gas switch off.

I am now wondering exactly what the electronic control module in the unit does and will look for a wiring diagram online.

[WhittleBurner]

Have you considered that maybe the switch is upside down and you think it's off but really isn't. Also ,I could be wrong but thought the light only lights if there is some sort of fault with the gas

[wdonovan]

Switch is not inverted. Up is on, gas is on, light is on. Down is off, off. All illuminated switches on the panel light when switch is on, They are not fault indicators.