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Furnace Issue

Troutmaster1972
Explorer
Explorer
So I'm at the end of my rope. Atwood 8531-iv furnace in a 2005 Max Lite. Furnace started intermittently running ok and then not running at all. When it didn't run, it would start the fan, ignite the burner, run and pump hot air 5 or 6 seconds, then lose flame and retry two more times doing the same thing and lockout throwing an ignition fault code.Figured it was probably the flame sensor so I pulled the unit and replaced the ignitor/flame sensor and put a new burner in since I had it out. Ran good for one night, cycling as it should then started doing it's old tricks again. If I understand how this works correctly, since it's starting up and burning 5 or 6 seconds, it shouldn't be the sail switch or control board. Am I correct in this assumption and if so does anybody have a clue what else it could be? Also should mention I have a brand new thermostat I just put on.Thanks in advance for any help!
11 REPLIES 11

joebedford
Explorer III
Explorer III
Low battery?

3_tons
Explorer
Explorer
This is a great conversation, I would only add that the distance between the igniter and it’s contact should be about 1/4”…I had the same problem as OP and found that over a time this distance had spread due to vibration - after narrowing this gap, problem solved!

3 tons

JBarca
Traveler
Traveler
Troutmaster1972 wrote:
So I'm at the end of my rope. Atwood 8531-iv furnace in a 2005 Max Lite. Furnace started intermittently running ok and then not running at all.

When it didn't run, it would start the fan, ignite the burner, run and pump hot air 5 or 6 seconds, then lose flame and retry two more times doing the same thing and lockout throwing an ignition fault code.

Figured it was probably the flame sensor so I pulled the unit and replaced the ignitor/flame sensor and put a new burner in since I had it out. Ran good for one night, cycling as it should then started doing it's old tricks again.

If I understand how this works correctly, since it's starting up and burning 5 or 6 seconds, it shouldn't be the sail switch or control board.

Am I correct in this assumption and if so does anybody have a clue what else it could be? Also should mention I have a brand new thermostat I just put on.Thanks in advance for any help!


Did you ever get this sorted out? I restore older campers in the age range of yours, and the Atwood 8500 series -IV is common during that time period. See if any of this helps.

You mentioned it threw the flame fault code blinking lights. That is a big key piece of info. A few things:

Your new T stat should not be part of throwing an ignition code. While the T stat could be acting up, opening intermittently, it only pulls the run signal and shuts the furnace down; it is not linked to the ignition code that the control board detected. So this helps rule out the T stat, or if you have the Dometic AC ducted system, the heat interlock in the AC control board could interrupt the furnace run signal.

The ignition code points to the flame sense acting up or the gas supply acting up. If the gas drops out, the flame sense will see it.

Since you changed the igniter, that helps rule out the heavy rust that can form on the male spade connection to the high voltage wire over time and create resistance to mess with the flame sense circuit. BUT, how did the female connector look that joins the new spade connect to the new igniter? If the female end on the cable is really bad, that is a possibility of creating high resistance that the spark voltage can jump through, but the flame sense is having issues.

You mentioned it shouldn't be the furnace control board. Well, not necessarily. Half the board may be working, but the flame sense feedback is not; the board is still suspect, and the connections to the board.

The gas supply, I have had to replace many of the gas valves, but so far, all were due to leaking. I could not pass a 3 or 5-minute leak test with the gauge reading the bleed down. Corrosion in the aluminum valve seat, I believe, is the issue. Too many hot and cold cycles from the winter and the bare aluminum sweats. I passed the test until I fired the valve; then, it would always fail the test. A bubble leak test on the tip of the gas jet confirmed it was leaking. This is on a bench test when servicing the furnace. I have not yet found a valve coil failure, but it is not beyond one of them acting up.

At this point, you are left with this in the order of probability.

1. The PC board is bad, or the connections on the board.
2. The high voltage wire female connection is bad at the ignitor.
3. You have a gas valve issue. You can test the valve with a bench test by doing a bubble leak at the gas nozzle tip. It should not stop blowing bubbles when energized. They do still sell the valve for the IV vintage furnace or did 4 months ago.
4. I never heard of the bad propane messing with the flame sense; that is a new learning.

Let us know how this comes out.

John
2005 Ford F350 Super Duty, 4x4; 6.8L V10 with 4.10 RA, 21,000 GCWR, 11,000 GVWR, upgraded 2 1/2" Towbeast Receiver. Hitched with a 1,700# Reese HP WD, HP Dual Cam to a 2004 Sunline Solaris T310R travel trailer.

John_Burke
Explorer
Explorer
Flame sensors rods can get a film covering them from not so clean propane and switching from one propane dealer to the next regularly or going back and forth from propane to butane. Not saying the propane is dirty or bad just there may be additives is some of it. I have had the same problem on an RV furnace and my home furnace when we switched from propane to natural gas. I pulled the flame sensor out of both units and used emery cloth to clean the rods up and no more issues.

wa8yxm
Explorer
Explorer
Flame sensor failure... On most of these the flame sensor is also the spark rod. During IGNITION it has about 1,000 volts AC on the wire. then it swiches over to Flame Sense.. that's (ROunding shamlessely) about 1/2 volt DC.. Can you see a possible problem if the switchover goes funny and the last of the thousand volts hits that senisitive chip? Chips a poppin that's for sure.

Now it can no longer sense flame

So I got a new control board from Dinosaur boards.. First thign I noticed when I opened the box (I'm trained in electronics) Was that it was one quality board. Very well built. Solid plating of the traces. Well done.

Then I turned it over to the component side and right about next to where I thin that sensor chip is there sat what is called a Gas Discharge Tube (Like a NEON night light bulb.. in fact I suspect that's what it was The standard NE2 Neon bulb limits voltage to 90 DC at that point it lights up and sunts that thousand volt spike to ground protecting the chip.. Worked too.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times

johnhicks
Explorer
Explorer
Bad limit switch maybe? You'll probably have to pull the unit to get at it.
-jbh-

enblethen
Traveler
Traveler
There should be two coils on the gas valve. Separate the wiring and read coils individually. Coil resistance should be nearly the same.
Is the ignitor wire tight to the circuit board coil? Check the high voltage wire for an nicks or damage.

Bud
USAF Retired
Pace Arrow


2003 Chev Ice Road Tracker

Troutmaster1972
Explorer
Explorer
Yeah snapped on tight. I was real light with the steel wool. I'll try an eraser next.

enblethen
Traveler
Traveler
Steel wool was a bad choice! You could have damaged contact material. White pencil eraser would have been better. Did the connector go back on tight?

Bud
USAF Retired
Pace Arrow


2003 Chev Ice Road Tracker

Troutmaster1972
Explorer
Explorer
I did clean the contacts with a little bit of steel wool. Didn't apply anything to them though.

enblethen
Traveler
Traveler
Did you clean the multi-wire connector on the circuit board? Should be cleaned and a de-oxidation compound applied to contacts.

Bud
USAF Retired
Pace Arrow


2003 Chev Ice Road Tracker