Furnace does not light

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timjet

Well-known member
Joined
Aug 7, 2012
Posts
389
Location
Tampa Bay
Atwood hydro flame 8500-IV series Furnace does not light. Blower comes on for about a minute then stops. I can smell propane at the unit while the blower is running. I do not hear a clicking sound,so I'm assuming no ignition. The circuit board diagnostic LED indicates a "Flame Sense Fault".

I removed the ignitor. It looked new, apparently the unit has not been used much here in south Florida. I cleaned it and checked the gap at 1/8". I checked the voltage on the ignitor and got 12v while the blower was on. Seems like it should be greater than 12 v to spark a 1/8" air gap.

Any Suggestions??
 
Do you see the spark at the ignitor?? Do you hear it go tick . . . tick . . . tick. Check the orifice. Spiders will get in there and spin a web. You may smell gas but it might not be getting to where it needs to go.

 
I removed the ignitor, cleaned it, sand papered the contacts and used mineral spirits to clean any sand paper residue. With the ignitor out of the unit, I reconnected the red wire to the ignitor and grounded the base. Turned on the furnace, blower came on as it should but no spark. Everything around the unit looks clean, no spider webs or mud dobbers.
 
That fault code sounds like it could be a thermocouple problem.  It tells the controller that the flame is actually lit, so that gas doesn't continue to flow if it gets blown out or won't light.  If you can find it, be sure it's in the flame and not all sooty, broken or disconnected. 
 
I see two "Suspects" 

1: Spark gap.  I would give you an off hand gap but .. Well it's been 7 years since I did this so check the owner's manual.

2: Control board.. That is what generates the spark. I recommend DINOSAUR boards if you need to replace it.

OH, and a 3rd, the wire that connects the two (Dirty connections) howev er the odds of that being the issue (since you hear no spark) approach zero.

The other suspect is the blower speed. but you said you smelled propane so I will assume it is coming up to speed and the sail switch is sailing..er. closing .
 
Problem found and fixed. The control board was faulty. I swapped the control board with the other furnace and it worked. I ordered a new control board from Amazon installed it yesterday and it works. Incidentally my furnace is a 2 stage type and has 2 control boards, one for the 2 stage blower and the other that controls everything else on the furnace. The smaller 2 stage control board is fine. I think the only thing wrong with the faulty board was the ignitor coil. It can't be replaced.

DINOSAUR electronics does not make a control board for furnaces with a 2 stage blower.
 
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