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Robert, RV Mechanic
Category: RV
Satisfied Customers: 12788
Experience:  18 yrs. RV experience including Cummins North West, Country Coach, Monaco Coach - vendor certified.
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Have a Duo Therm Camping trailer furnace that will not light

Customer Question

Have a Duo Therm Camping trailer furnace that will not light to produce heat.
Paid funds for a Tec to repair. After his working on unit I installed back in GMC Motor home. Furnace did not produce heat. I removed and took it back for repair. The Tec bench tested and it seemed it was not going to light and produce heat. After he put it on a new battery the furnace lite and produced heat for a short time. Tec indicated he could only clean the sail switch connections. he claimed the new switches were not available.
Got on line and found a new switch. Believe it has been installed correctly. Got propane going to furnace. have by past the thermo stat. Blower seems to be working correctly.
Sail switch should be working. Have a green light lit around board. no flame or heat.
Submitted: 3 months ago.
Category: RV
Expert:  Robert replied 3 months ago.

Hi my name is Robert....

After the fan comes on does it try to spark at ALL???


Expert:  Robert replied 3 months ago.

IF it is sparking IT is NOT a problem with the sail switch, high limit or thermostat.

The fan will blow on that sail switch and when it closes it passes a signal to the circuit board, once the circuit board sees that signal then it will spark.

IF you had low voltage or a faulty sail switch it would never spark. IF you have power through the sail and high limit to the board and it is not sparking then you have a bad circuit board or electrode.

Make sure your battery voltage is good as well, I read the part about the new battery, if the voltage was dropping under 11.5 volts the fan may not spin fast enough to close the sail switch.

IF it is sparking please let me know, it matters on how to diagnose these if it is sparking or NOT.... Robert

Customer: replied 3 months ago.
Apparently it is not sparking sound
Customer: replied 3 months ago.
Lets conduct by email
Believe I have paid enough funds
Need to be satisfied for dollars spent by email
Expert:  Robert replied 3 months ago.


What is the model of the Duo therm? I can send you a service manual, you need to see if power is getting to the circuit board via the sail switch, if you have no power then the furnance is not going to spark, if you have power then this is going to be a bad electrode or circuit board. Most RV shops have a special board tester and can tell if the board is bad or not. The tech should have tested the board out, but if he told you there was not a replacement for the sail switch then I would not count on anything he did.... Robert