RV Furnace won't light

Thread starter #1

SCPO

Senior Member
I was deer hunting this week with cold weather. Turned my furnace on in camper. Blower came on but it did no light. 30lb propane bottle full. It is a Atwood 8500. Any suggestions on what to look at
 

bany

Senior Member
Mine wouldn’t light one trip. It was pretty chilly or cold but especially wet out. After getting some dry heat via other source it worked. Not sure it still works though, maybe I’ll try it out today. Been using electric heater.
 

Cook&Bro

Senior Member
Checked Google:

http://www.irv2.com/forums/f54/atwood-furnace-not-igniting-238964.html

From that link:

Got tired of typing this so saved it as a text file....

When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps by the way So does bad wire/connection.
Not an 8500 series, but might be helpful. The circuit board apparently has a diagnostic light - fault codes.
 

Cmp1

Swamp Yankee OABA Recipient
If it has a sail switch it's either the switch sticking,or the Inducer motor,,,,
 

Cmp1

Swamp Yankee OABA Recipient
If it has a sail switch it's either the switch sticking,or the Inducer motor,,,,
The switch tells the board that the Inducer motor is running and to light up the igniter
 
Thread starter #8

SCPO

Senior Member
thanks for info. don't know when I can go back. Came home Friday with Flu.76 years old and didn't get a flu shot. My wife kept reminding me that she told me to get one
 

Cook&Bro

Senior Member
Thread starter #10

SCPO

Senior Member

Cmp1

Swamp Yankee OABA Recipient
If the Inducer motor is running and the switch is made,and no ignition,pull the igniter connector and check for voltage,,,,
 

Cook&Bro

Senior Member
If it has a sail switch it's either the switch sticking,or the Inducer motor,,,,
Couple of interesting sail switch details from internet search;

(1) if DC voltage is low, blower rpm will not be adequate to make sail switch, and

(2) intake or exhaust restrictions will have the same effect. Common cause of restrictions - mud daubers. Yep.
 

3ringer

Senior Member
Can you hear the igniter trying to light. It will make a clicking sound. You may just have air in the lines . Try lighting the stove to purge the air pockets. Try lighting the heater again with the stove lit. Also could be a bad propane regulator.
 

Cmp1

Swamp Yankee OABA Recipient
When you get back to it you should grab some pic's,,,,how old is the unit,,,,pull the cover and take some pics,,,,check for a birds nest in the exhaust,,,,
 

shdw633

Senior Member
When you get back to it you should grab some pic's,,,,how old is the unit,,,,pull the cover and take some pics,,,,check for a birds nest in the exhaust,,,,
Hornets nest as well. I had that once and couldn't get my unit started. Pulled the plate, found and cleaned out the nest and she fired right up.
 
I work in an Rv Shop: 90% of the time if the blower comes on but there is not tick, tick tick following it , it is the sail switch...easy to replace..may have to pull the furnace depending on how the factory installed the furnace.

If fan comes on, and there is an audible loud click once then the gas valve is opening which indicates the sail switch and control board are functioning properly. (Either the chamber is blocked(wasp nest,dirt dobbers, or ignitor are inop)

Hope its the 1st, cheap and easy to replace. Good Luck
 
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