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R & K RV
R & K RV, RV Mechanic
Category: RV
Satisfied Customers: 194
Experience:  Many years of experience on all types of RV repair. Specializing in electrical and generation.
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The suburban forced air furnace in the RV will not ignite.

Customer Question

The suburban forced air furnace in the RV will not ignite. The fan comes on but will not light.
Submitted: 7 years ago.
Category: RV
Expert:  R & K RV replied 7 years ago.
It sounds like your control board has gone bad. If it is the original board, it has lasted much longer than most do.
Its function is to open the gas valve, send high voltage to the ignitor, then receive a signal back from the flame sensor to tell the board that a flame has been established. Once the thermostat is satisfied, it will shut off the 12 volts to the board and close the gas valve.
There are a couple of safetys before the board gets 12 volts that may also be the problem but it sounds like the board. Since you say that the gas is getting to the burner, the board is doing part of its job.
A few seconds after the blower starts, you should hear a clunk (gas valve opening) then a rapid clicking which is the ignitor coil on the board sending high voltage to the ignitor wire. Can you listen at the furnace and tell me if you hear any of these sounds? Also, do you have a 12 volt test light or a volt meter to check for 12 volts at the control board?
If you can you give me the model number from the furnace, I will link you to a service manual.
Let me know and we can go from there.
Thank you,
Customer: replied 7 years ago.
The number is XXXXX to read. Maybe NF 24M.
Expert:  R & K RV replied 7 years ago.
It is probably a NT24M. There were three different models of this furnace due to the type of gas valve that they used. Essex, Harper-Wyman, and Johnson-Fenwal were the different valves used. They will all work the same so the wiring diagram will be the same.
HERE is the service manual for most of the NT series. It gives some good troubleshooting advice and the wiring diagram is on page 16.
If the gas valve is opening and you do not hear the rapid clicking, the board will be bad. You will probably need to get near the furnace to listen as the clicking gets faint as the boards get older.
Dinosaur Electronics make a universal replacement for your board that is far superior to the OEM and around half the price. You can purchase one for around $95-$100.
Let me know if you have any questions and I will be happy to assist.
Thank you,
R & K RV and 2 other RV Specialists are ready to help you
Customer: replied 7 years ago.
We will give it a try. Thanks
Expert:  R & K RV replied 7 years ago.
Thank you for the Accept. Please let me know if you need further assistance with this matter. You can come back to this same post if needed.
Have a good evening,
Customer: replied 7 years ago.
Thank you for your input. It was indeed the board as you suggested. We had a repair man fix the problem as his work is guaranteed. Thank you so much.
Expert:  R & K RV replied 7 years ago.
You are very welcome. Thanks for using JustAnswer.

Thank you for the Accept. Please leave feedback for me as it is a vital part of our ratings.
I will do the same for you.
Thanks again,