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
