How to start camper furnace model no 7920-11 - RTO Atwood Water Heater - 6 Gal LP

Not sure but its possible your thermo coupler is shot and needs replacing. If you have a pilot light it could be out but the furnace should not start if the pilot is out as there should be no oower getting to the controls unless the pilot is trying to let it start. A bad thermocoupler will not let the flame start.

Sounds like it may be a dirty flame sensor. It can be gently cleaned with steel wool or scotch bright pad (not emery or sand paper). Its a small rod that sits in the flame. I believe it is part of the spark ignition assembly on your model. Only open your burner compartment though if your are certain you have the skills (and perhaps gaskets etc) to reassemble it safely.

God bless

Is there a switch or a GFCI in the circuit between the breaker and the unit?

Copy following link:
http://waterheatertimer.org/Atwood-water-heater-resources.html
Otherwise there are 100s of atwood water heater resources on internet covering the different models old and newer

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Your electrode acts as flame sense as well. Remove electrode and clean it thoroughly/carefully especially at end where flame would be sensed and retry. Be sure connections on high tension wire is good and clean as well as connector and contacts on circuit board as well. If still same result, replace electrode.

That is hard to answer but I would say that for a furnace of that size you are probably looking at somewhere around 16x20x1. On older heil furnaces they often had the filter mounted inside the blower compartment so if the case you can just remove the cover and measure it. If not it should be located on the return air duct close to the furnace. Hope this helps you some. Thank you.

Is there a booster motor for the burner? I have seen these stick and make a furnace not turn on. The thermostat trips and you hear the furnace click on but nothing else happens. The booster is a small electric motor connected to a small duct. Take the booster motor loose and turn the fan by hand. Usually they will start working after you do this. Make sure furnace is shut off when you do this. Some booster motors have ports to oil them also.

is installed in a vertical up flow or horizontal position , if in horz position you could have a bad or miss positioned roll out switch this is a thermal switch positioned toward the burner edge that if the flame rolls out of burner area trips and then resets as it cools allowing the furnace to re-start until it reaches temperature , something to check .

look under camper at floor