Atwood Furnace - Ignition Lockout Fault

[braygor]

When I turn on the furnace, blower comes on for a few seconds, then the gas and ignitor - it ignites and burns for about 5 sec (with ignitor clicking entire time), then gas and ignitor shut off, blower continues for 10 seconds, then it cycles two more times, then shuts off. After that, the LED on the board blinks 3 times, indicating Ignition Lockout Fault. I have good gas flow and it's clear that the gas is igniting, as I get hot exhaust. I changed the control board because that seems to be a common fix and it's pretty easy (just not on the wallet). Unfortunately, that didn't do it. So I'm thinking the board is not getting the message that the gas is igniting, which leads to thermocouple. Anyone familiar pulling one of these out? Is the thermocouple built into the ignitor?

[braygor]

Success! The new ignitor works. Furnace comes on after 2-3 ignitor clicks; ignitor then stops and furnace continues running as is expected. The new control board was an unnecessary expense, but it was still less expensive than taking it to a repair shop. And it never hurts to have a spare control board.
Thanks to all for your input.

[braygor]

I removed the burner assembly tonight. Mud dauber nests all packed in there out of sight. On the igniter base and wire contacts. I reset the gap to 1/8" reinstalled, and now have less success than before. Gas comes on, but the igniter doesn't click. May have damaged the igniter in setting the gap and/or cleaning mud off it, but that's an inexpensive part. The burner was in decent shape, but I'll go ahead and replace it while I have it apart.

[enblethen]

That somewhat rules out a bad regulator. If you had low pressure and volume the flame would have flicker with yellow flame.
At the furnace, locate the two blue wires on the terminal strip. Connect them together there rather than at the thermostat test as suggested in my other post.
The colors leaving the furnace should be the two furnace wires at the thermostat.

[braygor]

enblethen wrote:
colors appear to be correct with provided model number.
How does the stove top flames look? Turn on all and see if flame turns yellow. This is sign of bad regulator.
Check electrode for proper spacing.
Remove cover from the thermostat. check how many wires. If only two wires connect them together. Furnace should cycle on and provide heat with no shut down. Separate the two wires, furnace should go into cool down mode and shut down.

I can run all three burners with blue flames. Oven worked well this weekened too.
Thermostat has six wires (red, blue, yellow, green, white, gray.

[BFL13]

Watch for the screen on the "burner" (tongue looking thing) being rusted out in spots or big chunks of it. That messes up the flame that the sensor above the screen feels. You can get those burners on Amazon.

[enblethen]

Before you tear apart furnace, test the thermostat

[braygor]

wa8yxm wrote:
Ok Starts. then shuts off (3 times) then locks out Each time it lights but then shuts off.. Sounds very very very familure (As in I had that problem).

Suspect list:
An obstruction in the burner orifice (Gas jet) or elsewhere can cause a weak flame. I do not think this is it

A deffective thermocouple may not detect the flame. I've heard of this but again I do not think it is common.. If it's all cruded up with carbon it might be and issue.

Bad connection between Thermocouple and mother board (NOTE on a single wire system the wire is the ignition wire) this can do it. After all ignition is like 1000 volts AC and Sense is 1/2 volt DC so the kilovolt will overcome a bad connection and actually make it worse.. However again I think rare.> Still easy to check (just pull and reconnect the connectors a few times each one on each end of the wire)

Bad control board (Motherboard) DING I found my winner..
THeory (And support to follow) is that if the swichover from SEND SPARKS to Look for .480 volts from thermocouple goes flakey then the sensor chip gets hit with up to 1500 volts and POP goes the wafer. So no heat sense.

Solution was a new board from DINOSAUR boards.

Support for my theory: ON the Dino broad right about where I suspect that sensor chip is there is a nifty gas discharge tube. This tube is a "Surge Suppressor" type device (like the MOV in a power strip) that clips and limits the voltage to something the sensor chip can withstand.

My Guess is that Dinosaur Boards and I think alike on this issue.

Other comments: I am a trained Certified Electronics technician who has designed and built some of his own hardware. My initial impression when I took the Dino board out of the box was QUALITY!!!.. and nothing since has changed that impression .. Oh that was 2012 (Feburary) when I opened that box. it still works.

Great info, thanks! I replaced with an OEM board last Thursday morning, because it was all that was available locally and we were heading out Thursday afternoon. While I'd prefer the Dino board, the brand new OEM board is giving the same issue, so I don't think it's a board issue. Next step will be to pull the ignitor/burner assembly, check all connections, spacing, carbon build-up, etc.

[enblethen]

colors appear to be correct with provided model number.
How does the stove top flames look? Turn on all and see if flame turns yellow. This is sign of bad regulator.
Check electrode for proper spacing.
Remove cover from the thermostat. check how many wires. If only two wires connect them together. Furnace should cycle on and provide heat with no shut down. Separate the two wires, furnace should go into cool down mode and shut down.

[braygor]

enblethen wrote:
Check the alignment of the flame senor to insure it is directly in the flame.
Black should be ground
red goes to gas valve
white to limit switch
blue connects to the blue from limit switch that ties to the thermostat.
This is according to furnace manual I have.
Exact model of your furnace would help!

Thanks for all the info. Model is Atwood 8525-IV DCLP

[wa8yxm]

Ok Starts. then shuts off (3 times) then locks out Each time it lights but then shuts off.. Sounds very very very familure (As in I had that problem).

Suspect list:
An obstruction in the burner orifice (Gas jet) or elsewhere can cause a weak flame. I do not think this is it

A deffective thermocouple may not detect the flame. I've heard of this but again I do not think it is common.. If it's all cruded up with carbon it might be and issue.

Bad connection between Thermocouple and mother board (NOTE on a single wire system the wire is the ignition wire) this can do it. After all ignition is like 1000 volts AC and Sense is 1/2 volt DC so the kilovolt will overcome a bad connection and actually make it worse.. However again I think rare.> Still easy to check (just pull and reconnect the connectors a few times each one on each end of the wire)

Bad control board (Motherboard) DING I found my winner..
THeory (And support to follow) is that if the swichover from SEND SPARKS to Look for .480 volts from thermocouple goes flakey then the sensor chip gets hit with up to 1500 volts and POP goes the wafer. So no heat sense.

Solution was a new board from DINOSAUR boards.

Support for my theory: ON the Dino broad right about where I suspect that sensor chip is there is a nifty gas discharge tube. This tube is a "Surge Suppressor" type device (like the MOV in a power strip) that clips and limits the voltage to something the sensor chip can withstand.

My Guess is that Dinosaur Boards and I think alike on this issue.

Other comments: I am a trained Certified Electronics technician who has designed and built some of his own hardware. My initial impression when I took the Dino board out of the box was QUALITY!!!.. and nothing since has changed that impression .. Oh that was 2012 (Feburary) when I opened that box. it still works.

[doxiemom11]

We had to change the circuit board when ours did that.

[enblethen]

Check the alignment of the flame senor to insure it is directly in the flame.
Black should be ground
red goes to gas valve
white to limit switch
blue connects to the blue from limit switch that ties to the thermostat.
This is according to furnace manual I have.
Exact model of your furnace would help!

[braygor]

BFL13 wrote:
Model/year of the furnace? Some have separate heat sensor probes going to the circuit board, while the newer way just has the sparker, but it "reads" the flame magically, so your post is not clear on that. You changed the CB and it did not fix it, so is it the old way you can change the probe that lies alongside the sparker?

That flame sensor probe ( if fitted) has its own wire that can be checked for connection too.

Trailer is 2006, furnace is original. CB has four connections - the harness, one to the black cylinder (spark?) and two small lines, one red and one blue.

[A1B00902]

Same thing happened with me, each year before we go south,but after 3 tries it stays on, I think that the igniter was damp/dirty, after it dried it worked.