Furnace flames cycles off before temp is reached

[Chief_Bob]

I have a new to me 2018 Thor Aria 3401. On our first long trip and we needed the furnace. When it starts the flame starts as it should. The flame continues for around 10 minutes and then the flame cuts off as though it reached the thermostat temperature, but it hasn’t. The fan runs about 5 minutes and then the flame comes back on and the furnace continues heating.

I would appreciate any suggestions on where to start looking. I know some safety is cutting off the gas because something is probably too hot. I just don’t know where to start.

Thanks

[Chief_Bob]

Thanks

[pushtoy_2]

not enough air flow check for restrtion some where or the blower isnt moving enough air.
check for low voltage. i had the same problem but on a older coach. i would check the voltage first thats ez.

[Chief_Bob]

Thanks

[CavemanCharlie]

Chief Bob wrote:
Got back from our maiden voyage and spent some time on the furnace. Check the intake and discharge ducts. Found lots of saw dust in the floor ducts and even the cutout piece of plywood they didn't bother to remove. Blew out the blower wheel and intake. We made sure nothing is in front of the intake in the bathroom. The air volume is good on each discharge and I even removed the dampers on the floor grates so they don't get accidentally closed. There are only 3- 4" discharges on the furnace, pls a 2" for the basement. I did not clean the control board terminals but I will need to because it still short cycles.

I've never heard of it causing Short Cycle problems. But, wasps love to build nests in the furnace exhaust and intake ports on the outside of the RV. I've had 2 different campers where I had to clean the ports out to get the furnace to work. Once I had to remove the furnace and I ended up dumping a whole coffee can full of wast nest material out of the furnace. You might want to check it out !

[Chief_Bob]

Got back from our maiden voyage and spent some time on the furnace. Check the intake and discharge ducts. Found lots of saw dust in the floor ducts and even the cutout piece of plywood they didn't bother to remove. Blew out the blower wheel and intake. We made sure nothing is in front of the intake in the bathroom. The air volume is good on each discharge and I even removed the dampers on the floor grates so they don't get accidentally closed. There are only 3- 4" discharges on the furnace, pls a 2" for the basement. I did not clean the control board terminals but I will need to because it still short cycles.

[jls]

I have found that setting something near the furnace will block enough heat that the furnace will act like yours

[enblethen]

Another thought!
Have you removed the circuit board, cleaned the contacts with a white pencil eraser applied some de-oxidation compound then reinstalled? It is possible that the problem could be there.

[Chief_Bob]

Thanks

[enblethen]

Could be as easy as a loose connection within the furnace. Heats up and goes open!

[Chief_Bob]

One thing I have been able check on the road is that when the flame short cycles the thermostat is still calling for heat. Thanks

[Grit_dog]

Chief Bob wrote:
Thanks all. I’m touring bourbon distilleries in Kentucky today so I’ll have to get the model tonight .

I wouldn’t be able to read a street sign or type my own name after touring bourbon distilleries!!

[C_Schomer]

I'd use a meter and determine what's doing the cycling, first, stat or hi limit. Check the temp rise. I've never had short cycling problems with my RV furnaces but I like to see no more than 70* degrees rise in a res. furnace, when the airflow is really good. Make sure the flex ducts aren't kinked, stat in warm air current, clean the blower wheel, dragging motor, etc... normal checks and maintenance. Craig

[Chief_Bob]

The furnace is an Atwood 35,000 btu model AFMD35151.

[wildtoad]

Chief Bob wrote:
Thanks all. The furnace is an Atwood. I’m touring bourbon distilleries in Kentucky today so I’ll have to get the model tonight. We should be out of the freezing overnight temperatures for the rest of the trip so hopefully we’ll get by with the heat pumps. I’ll pull things apart and check for obstructions when we get home. I always count on this forum for good advice and direction.

Make sure you go by Buffalo Trace.