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Robert, RV Mechanic
Category: RV
Satisfied Customers: 13510
Experience:  18 yrs. RV experience including Cummins North West, Country Coach, Monaco Coach - vendor certified.
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Atwood heater-model 8535-IV DCLP: I turn on the thermostat

Customer Question

Atwood heater-model 8535-IV DCLP : I turn on the thermostat to furnace, fan to auto, (and on LO), push temp to 90, fan starts, shuts off after approx. 30 secs, but furnace won't fire. Outside I removed the furnace cover and flip the reset switch. A friend watched the panel while I repeated the process inside. He said the diode on the circuit board showed 1 w/ 3 sec. pause (air flow limit fault). Is there anything I can do? Do I need to call someone? Thx
JA: Have you checked the coolant level? Has there been any leaking from the hoses?
Customer: The guy from the propane company came and hooked me up, bled the air from the lines by firing up the stove (flames blue and constant), then the h20 heater (has run well since yesterday), but he was stumped that the furnace would not fire.
JA: What is the model of your '90 RV?
Customer: Pilgrim Legends (see initial post for furnace model #)
JA: Are you fixing your RV yourself? What have you tried so far?
Customer: Check 2nd post
JA: Anything else you want the mechanic to know before I connect you?
Customer: The 4 posts should explain all
Submitted: 11 months ago.
Category: RV
Expert:  Robert replied 11 months ago.

Hi my name is Robert.....

IS the electrode sparking? After the fan comes up to speed you should hear a click from the gas solenoid valve and the electrode will start to spark....


Expert:  Robert replied 11 months ago.

Let me know if you still need help on this, it matters if it is sparking or not on which way to diagnose... I suspect if you have that fault it is NOT sparking, let me know, I am around daily and respond when I can... Robert

Customer: replied 11 months ago.
I suspect that it was not sparking as I was inside at the thermostat and he saw the diode an air flow fault. Also, once the blower went off, nothing happened
Expert:  Robert replied 11 months ago.


So as the fan comes up to speed it will blow on a sail switch which sits inside the blower wheel, once the sail switch closes it passes the signal through the high limit to the board. Once the board gets the signal it will allow the electrode to spark and the gas valve to open up.

IF you are getting voltage on that signal wire then it sounds like a board issue, most RV shops have a special board tester and can tell if it is at fault.
IF you have NO voltage at the circuit board then the sail switch or the limit switch is suspect. Check your battery voltage as well, IF the voltage was low say 11 DC or under the fan would come on but would not spin fast enough to close the sail switch, so make sure you have over 12 VDC.

I can get you a wiring diagram if you like so you can see where to check voltage but you will need a volt meter. IF you do not have a meter and your battery voltage is above 12 volts about all you can do is have the board tested or have a RV mobile or shop take a look... Hope this makes sense. IF you would like a service manual let me know, no extra charges... Robert

Customer: replied 11 months ago.
I suspect that the board may have a problem. But is that the problem when the diode on the board signaled an air flow fault. BTW, just answer tried to charge me an additional $42. I cancelled, but I wanted to make sure, do you have a # I can call them?
Expert:  Robert replied 11 months ago.

You need to see if voltage is getting to the board thought the sail and limit switch, if the board is getting voltage then yes board, if the board is not getting voltage then no, sail switch or limit switch issue, let me get you a wiring diagram...

I do not handle the payments, billing etc, click HERE for customer service....

Expert:  Robert replied 11 months ago.

Click HERE for a service manual. You should have voltage on the white wire at the board if the circuit is complete, no voltage on that wire, no spark.

If you are satisfied with my efforts please feel free to select a star rating on the page, it is the only way I get "credit" for helping... Robert