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

[JimK-NY]

Mine also runs about 10 minutes, then the flame cuts out for a few minutes and the cycle begins again until finally reaching the temperature set by the thermostat. This is something I hardly notice unless the temperature is cold and I am impatient for the heat.

[Grit_dog]

^Very helpful.

[time2roll]

I added two new ducts to increase airflow. Burner cycled about every 3 minutes before, runs continuous now until the thermostat is satisfied. Provides more heat also.

[Chief_Bob]

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.

[lenr]

We have owned a 27' bumper pull, a 27' fifth wheel with one slide, and a 37' fifth wheel with 3 slides. Every one of them had 4 heating registers. My point is that the 37' fifth wheel needs more but the industry is too cheap to put them in. The 37' was the only one to cycle like the OP. I absolutely believe that it is an issue of inadequate air flow through the furnace. It has not been an issue when the furnace is cycling to maintain a temperature. It only does it when the furnace runs for long periods such as raising the temperature in the trailer. I haven't decided if I'm going to try to improve the airflow. If it quits cycling the flame on a long run I will be concerned that the temperature switch is not protecting from an over heat situation.

[enblethen]

Mike134 is correct about working on 12 volts DC. If battery(ies) drop too low the burner will cut out and the fan will continue to run.

[Mike134]

prichardson wrote:
Sounds like it is cycling on the high limit which is an indication of an airflow problem. Make sure that nothing is restricting the return air and that all registers are open and unrestricted.

This is correct./\ /\ /\ /\
Be wary of internet troubleshooting......your furnace ALWAYS operates on 12V regardless if the power inverter/distribution is fed from shore power or battery.

[wildtoad]

First thing to do is make sure the output vents aren’t shut off. Some owners will close off vents to force more air out other vents. Open any vents closed or otherwise blocked. Check the return for blockage too. These furnaces need good airflow in and out to keep from overheating. I’ve read questions on versions sites about needing a filter on the return like us done on home units. While you would think so, the answer is no. So check if previous owner put in a filter on the return.

[prichardson]

Sounds like it is cycling on the high limit which is an indication of an airflow problem. Make sure that nothing is restricting the return air and that all registers are open and unrestricted.

[enblethen]

Make and model of furnace?
Are you connected to shore power or operating on battery(ies)?
Thermal cut out could be issue.
Have you verified all vents are open and clear of anything blocking them.
Properly installed system should not allow thermal cut out to operate unless there is a problem. They are a safety device!,

[richclover]

Fulltimer50 wrote:
The furnace has a safety feature that turns off the flame when it reaches an unsafe temp. The fan continues to run in order to lower the temp. Then the flame can come back on if the room temp has not reached the set temp. Your furnace is doing what it supposed to do. However I would make sure that there are no blocked heater ducts as low air flow can cause problems.

That’s exactly how mine works.

[wa8yxm]

First the flame WILL cut off before the blower on an RV furnace. this is so the furnace cools down

Second. Thermostats can be placed so hot air from the furnace hits them and "Fakes" them into thinking it'shot enough.. Check air flow to find if that's the case.

Third the T-Stat may have an adjustable "Anticipator" this device actually heats the T-Stat slightly in order to anticipate the residual heat in the furnace as it cools down. It may need adjustment. if that is it's adjustable.

[Fulltimer50]

The furnace has a safety feature that turns off the flame when it reaches an unsafe temp. The fan continues to run in order to lower the temp. Then the flame can come back on if the room temp has not reached the set temp. Your furnace is doing what it supposed to do. However I would make sure that there are no blocked heater ducts as low air flow can cause problems.