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Robert, RV Mechanic
Category: RV
Satisfied Customers: 13456
Experience:  18 yrs. RV experience including Cummins North West, Country Coach, Monaco Coach - vendor certified.
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How do you clean an Atwood 8940 furnace in a RV. The ...

Customer Question

How do you clean an Atwood 8940 furnace in a RV. The furnace will ingite, but after about 5 seconds, the burner will shutoff and the blower continues to run. It will try to ignite about about 3 times. Each time the furnace will burn for about 5 seconds and then the fire goes out.
Submitted: 9 years ago.
Category: RV
Expert:  Robert replied 9 years ago.

Hi There!

Thanks for Choosing Just Answer.

Allot of things to look at here below is the Atwood troubleshooting for the type of situation you are having. It sounds like the flame sensor is not sensing the flame. When this happens the gas valve closes so the flame goes out. Then the circuit board tries again to relite, and eventually goes into lockout. (3 strikes and you're out.)

The ignition probes and flame sensor need to be removed and cleaned and then see what happens. Check the igniter for any cracks.




  • Low gas pressure

  • Exhaust blocked
  • Combustion air wheel loose
  • Electrodes out of adjustment
  • Electrode defective
  • Circuit board defective


  • Flame sensor wire between electrode and
    circuit board defective
  • Air leakage at gaskets
  • Defective heat exchanger
    • Set pressure to a minimum of 11"W.C. with all appliances running. Replace regulator if not obtainable.*
    • Clean Exhaust*
    • Reposition wheel and tighten
    • Adjust electrode according to furnace specifications
    • Replace electrode
    • Clean plug contacts. If still defective, replace. (Check on board tester when possible).
    • Replace wire


    • Replace gasket
    • Replace heat exchanger




    Customer: replied 9 years ago.
    How do you remove and clean the ignition probes and flame sensor?
    Expert:  Robert replied 9 years ago.


    I am going to see if I have a manual laying around to better assist. This may take a few. Pretty much once you see the igniter you should see the flame sensor and flue, the flue can be blown out with low pressure air, the flame sensor and ignitor can be cleaned with steel wool, let me see if I have more info.

    Thanks, RJ

    Expert:  Robert replied 9 years ago.


    I am sending you a PDF which is allot of information because it covers all models. There is a breakdown of the 8940 near the end. According to this information the control board detects the presence of flame. IF this is not what you are looking for I can opt out for another expert. There is allot of great information and explains how each component works. You can view the PDF by clicking HERE.


    Customer: replied 9 years ago.
    Reply to RV help for u's Post: Still doesn't tell you how to clean the furnace. I'm thinking you have to remove the entire burner assembly to get to the electrode and flame sensor. Is that correct?
    Expert:  Robert replied 9 years ago.

    Good morning.

    Yes this is correct it is accessed by pulling the outside panel down and removing components. I did not mean to overwhelm you with so much information, I was hoping the breakdown of the furnace would give you an idea what you where up against. IF you do not feel comfortable pulling it apart I would have a RV shop tackle this project, cleaning everything may not even solve the issue. Normally I would expect an hour worth of labor for cleaning and troubleshooting the issue.