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Old 11-29-2010, 08:12 PM   #1
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Lennox 80MGF3-75A-3 Won't ignite


hello, I have a lennox 80MGF3-75A-3 that had a shorted out circuit board, I replaced the board. The a/c works fine, but when it was time to light the heater, it would not light. I put a new igniter electrode and flame sensor on, and yet I cannot get it to ignite. After four tries it goes into loockout and the yellow and red light blinks from one to the other. can someone help me with the situation.

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Old 11-29-2010, 08:24 PM   #2
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Lennox 80MGF3-75A-3 Won't ignite


describe the sequence that it goes through so we can determine what is not happening like it should, also does the board show a code other than lockout

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Old 11-29-2010, 11:26 PM   #3
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Lennox 80MGF3-75A-3 Won't ignite


Thank you for your response.
when the thermostat is set for heat, the red and yellow lights blink faster to inform a call for heat. The flue fan comes on then there is a sound as thought the ignitor is trying to light, but there is no spark or ignition. The only code is that watchguard, furnance failed to light.

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Old 11-29-2010, 11:32 PM   #4
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Lennox 80MGF3-75A-3 Won't ignite


are you sure there is no spark, you can remove spark electrodes and clean with steel brush or steel wool, also ensure orange ignition wire from board is plugged in properly
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Old 11-29-2010, 11:36 PM   #5
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Lennox 80MGF3-75A-3 Won't ignite


sorry just reread that you replaced electrode..... if there is no spark at electrode, then its the board if everything is plugged in

do you hear the gas valve open?
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Old 11-30-2010, 12:09 AM   #6
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Lennox 80MGF3-75A-3 Won't ignite


thanks hvactech126. The gas valve is opening. there is not a strong gas odor. there is a thump like sound after the ignitor fails to light. The ignitor cord to the board is tightly connected. The board was changed out earlier this summer with an upgraded brd.
on the old board, the yellow wire from the transformer was connected to the ground on the board. On the new board it is connected by itself. does this have an affect on the ground?
Every thing is working except the electrode ignitor. There is no spark. I checked the current from the board to the ignitor, and it showed 766. What problem exist. thank you.

Last edited by SAMUEL58; 11-30-2010 at 07:54 PM.
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Old 12-01-2010, 10:16 PM   #7
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Lennox 80MGF3-75A-3 Won't ignite


sounds like you need a new board, you should not be able to check voltage to that type of ignition system, it should be 10k volts or more
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Old 12-10-2010, 10:58 PM   #8
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Lennox 80MGF3-75A-3 Won't ignite


Problem solved! Thanks hvactech 126 for your help. I found the instructions for the new board, and every thing was connected correctly, however, there was a defect in the board itself.

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