I have the Atwood hydro flame furnace model #8531-IV 30,000 btu, using a Dometic Duo-therm thermostat.This furnace has been running very well up until this morning.Last night, as always, before going to bed I shut the thermostat off.Upon arising I switched the thermostat to furnace as always.Furnace within about 5-10 seconds blower started, ran about 10-15 seconds, igniter sparked lighting the burner, as usual.The burner burned about 3-5 minutes then shut off for about 3-5 min.did this several times.Thermostat set for 72* reading was 58*, outside temp was 48*,thermostat reading would not rise above 64*, turned thermostat to 82* temp inside did climb some but shut off before reaching set temp.Trying to isolate the problem. Thinking maybe thermostat or limit switch???? Need input for troubleshooting. Thank you

It is NOT the Tstat. It is an operational problem in the furnace internal controls. I would lean to a BAD Hi Limit switch on the furnace. The symptoms point to that. Doug

Toddupton wrote:Propane tank empty?Thank you for the idea. Checked the tanks and they are full with all valves turned on.

It's called 'limiting'High Temp Limit Switch is shutting burner down due to high temp and then when it cools down it refires.....cycle repeatsCould be temp rises too fast.....over firing due to high propane pressure (S/B 11" WC)Could be due to restricted discharge air flow.....too many registers closed off, collapsed duct work, obstruction/blockage in ductCould be due to insufficient return air flow.....obstruction/blockage at return air path or at furnace caseDefective High Temp Limit Switch.....have to pull furnace to access switchYour limit switch is L190 (190*F) part # 37022

Atwood furnace heating issues? | Good Sam Community

16 Replies

BrianinMichigan
Explorer
Feb 12, 2016
I have a similar problem with my 26 year old Atwood. It will heat up the motor home with no problem. But the flame keeps cycling on and off. I used a infrared thermometer to check the heat coming out of the exhaust and it would get up up to 275-300 degrees and then cycle off. it would cool down and then fire back up. I never felt that the heat would be as hot as it used to be coming out of the vents. I am still searching for the problem.
liborko
Explorer
Feb 12, 2016
I had very similar symptoms with my furnace. Replaced burner and firing electrode-works like a charm now. The burner was rusted & half of it gone.

burner: Atwood #30268
firing electrode: Atwood #34570
gotsmart
Explorer
Feb 02, 2016
You need a 2nd opinion. Get an indoor thermometer (something like the one below) and place it in the RV, where the heat isn't directly blowing on it. If the tstat is actually in a bad location for accurately reporting the temperature then the other thermometer will help show what offset is needed to achieve the desired temp.
Casinojunkie
Explorer
Feb 01, 2016
I believe it is the thermostat.
Question is, will a home analog stat work in its place?
I know I need one which will run the air conditioner and furnace.
Any ideas???
DrewE
Explorer II
Jan 31, 2016
My Duo-therm (analog slider) thermostat is very inaccurate in the temperature setting, at least for heat, and needs to be set somewhere around 8 or 10 degrees higher than the actual desired temperature. I would expect a digital thermostat to be somewhat more accurate.

You should be able to verify the furnace operation is correct by manually connecting the appropriate wires around the thermostat to force the furnace to run continually (until you undo the wire connection). If it doesn't cycle, that pretty well implicates the thermostat.
dougrainer
Nomad
Jan 31, 2016
Thoughts?
1. It depends on what type tstat(wall) you have. I suspect the tstat and/or the sensor for the tstat is not in a good location to sense the actual temp in the RV. You have it set at 72 but the location of the tstat or sensor senses 80 degrees at its location. Set the tstat at 85 degrees and see if the operation changes to 77 to 78 degrees as a set point. If so, your tstat and/or sensor is not in the ideal location. RV tstats have a plus or minus of 5 degrees. That is the range(error) per both RVP and Dometic. Doug
time2roll
Nomad
Jan 30, 2016
Fan and burner ran continuous?

Still you may consider a new thermostat.
Casinojunkie
Explorer
Jan 30, 2016
Casinojunkie wrote:
I have the Atwood hydro flame furnace model #8531-IV 30,000 btu, using a Dometic Duo-therm thermostat.
This furnace has been running very well up until this morning.
Last night, as always, before going to bed I shut the thermostat off.
Upon arising I switched the thermostat to furnace as always.
Furnace within about 5-10 seconds blower started, ran about 10-15 seconds, igniter sparked lighting the burner, as usual.
The burner burned about 3-5 minutes then shut off for about 3-5 min.
did this several times.
Thermostat set for 72* reading was 58*, outside temp was 48*,
thermostat reading would not rise above 64*, turned thermostat to 82* temp inside did climb some but shut off before reaching set temp.
Trying to isolate the problem. Thinking maybe thermostat or limit switch???? Need input for troubleshooting. Thank you

Update!!! This morning I switched on the furnace, temp was 60* inside RV, thermostat set at 80*. Furnace came on as normal, ran continually until 72* was reached and shut off, now it is running intermitly keeping temp at 72* while thermostat still set at 80*. What is your thoughts?
brulaz
Explorer
Jan 30, 2016
Had similar issue and it was a faulty regulator at the tanks.

It could release enough gas for the range and water heater, but the 35K BTU furnace's demands brought it to its knees. The furnace would click and sputter and then turn off. The problem appeared over the course of a day.

So would check the regulator first before pulling the furnace.
I believe the service tech attached a manometer (?) to a port in the range and monitored propane pressure when the furnace tried to run.

Actually, this may not be your issue as your furnace runs for 3-5 minutes? Mine would sputter for shorter periods, igniting briefly then dying.
ORbiker
Explorer
Jan 30, 2016
I had close to the same issue and needed to change the( 32) Burner Assembly. Pretty easy.

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Atwood furnace heating issues?

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