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Chief_Bob's avatar
Chief_Bob
Explorer
Nov 07, 2021

Furnace flames cycles off before temp is reached

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
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  • Mike134's avatar
    Mike134
    Explorer
    Nov 07, 2021
    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's avatar
    wildtoad
    Explorer II
    Nov 07, 2021
    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's avatar
    prichardson
    Explorer
    Nov 07, 2021
    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's avatar
    enblethen
    Nomad
    Nov 07, 2021
    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's avatar
    richclover
    Explorer
    Nov 07, 2021
    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's avatar
    wa8yxm
    Explorer III
    Nov 07, 2021
    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's avatar
    Fulltimer50
    Explorer
    Nov 07, 2021
    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.

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