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Old 10-28-2012, 03:15 PM   #1
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Lennox MGF80 Won't Light


The furnace blower comes on and the igniter goes through 3 attempts to light then goes to lockout. I have removed the flame sensor and all six burners and cleaned them. I reinstalled them and the problem still exists. However when I remove the burner in front of the igniter and the ignition cycle starts again, the furnace lights. The gas pressure checks ok and limiter switches all check ok.


Last edited by knappn; 10-28-2012 at 03:22 PM.
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Old 10-28-2012, 03:43 PM   #2
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Lennox MGF80 Won't Light


I don't get it.
Since the burner funnels the natural gas from the orifice to the opening of the heat exchanger, removing it results in open flame up the front of the furnace.

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Old 10-28-2012, 04:08 PM   #3
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Thanks for the response to my post.
The remaining 5 burners, to the left of the burner I removed, light just as they should with a nice blue flame. The sixth burner I removed remains unlit to the heat exchanger. This is the burner that has the igniter in front of it. When the burner is in it won't light. When I remove the burner with the igniter in front of it the the burners light. I was planning to replace the circuit board before I discovered that the burners light if I remove the burner in front of the igniter. Now I'm not sure. Any help is appreciated.
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Old 10-28-2012, 05:18 PM   #4
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Lennox MGF80 Won't Light


I am still not clear out your problem but many burners have a crossover that allows the flame of one location to reach all the others. It is usually a thin channel of metal running along the leading flame edge of the burners facing the exchanger.
Any small debris inside the crossover will stop the flame from lighting any burners beyond that debris stoppage. A thin strip of unfolded metal from a tin can will usually make a good tool for clearing out any crossover build up.
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Old 10-28-2012, 05:55 PM   #5
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I don't get it either.....ben sr
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Old 10-28-2012, 05:55 PM   #6
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I'll try to explain. My furnace has not been working for about a week now. I had two techs come to the house. One of the techs was a Lennox tech. They are not sure what is wrong. They both think it is the circuit board or the igniter. The Lennox tech wanted me to buy the circuit board for $711 and the igniter for $125. Then he would see which one fixed it. I can't afford to spend 711 on a circuit board so I found the circuit board at Cozyparts online for $298. However, before I spent that money, I decided I was going to do some troubleshooting myself to see if all I needed was an igniter. Yesterday I turned the furnace on and it started the ignition sequence. I heard the ticking of the igniter 3 seperate times before it gave up and went to lockout. I wanted to see what the spark looked like so I took the burner out that was blocking my view of the igniter and waited for the furnace to go through the ignition sequence and to my surprise it ignited. The five burners still in the furnace had a blue flame. The space where the igniter is and the burner was that I took out was dark. No flame. I turned off the furnace and put the burner back in. I turned furnace on again and the burners would not light. I turned the furnace off again and removed the burner and turned the furnace on and the burners lit. Why would the burners not light if there a burner (funnel) in front of the igniter but light if there is no burner in front of the igniter. I am confused. Any help is appreciated. Thanks so much for taking time to answer my posts.
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Old 10-28-2012, 05:59 PM   #7
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Lennox MGF80 Won't Light


anyway to get us a picture of burner assy...
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Old 10-28-2012, 06:04 PM   #8
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I believe I can. I'll give it a try.
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Old 10-28-2012, 06:28 PM   #9
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Lennox MGF80 Won't Light-image-2907297900.jpg
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Old 10-28-2012, 06:34 PM   #10
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Lennox MGF80 Won't Light


Unscrew the brass orifice for that burner and take the spider egg sack out.
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Old 10-28-2012, 07:00 PM   #11
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I checked the orifice and it is clear.
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Old 10-28-2012, 07:13 PM   #12
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Lennox MGF80 Won't Light


Still don't get it..
When you removed the burner, exposing the orifice to the atmosphere, and turned on the furnace so the other burners were burning, tell us what happened to the natural gas firing out the exposed orifice towards the flames?????
but anyways...
If the other burners will not ignite when one (ignition) burner is in place, then check if that burner is grounding out or deflecting the igniter spark.
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Old 10-28-2012, 07:18 PM   #13
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just a side thougth...is that a red warning tag in furnace saying unsafe condition......thats what they mean in pa and have to be removed by repairing company and signed off on????ben sr
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Old 10-28-2012, 07:35 PM   #14
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The flame comes off the igniter into the heat exchanger.
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Old 10-28-2012, 07:41 PM   #15
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No red tag stating that. There is a red tag saying gas supply must be disconnected during pressure testing.

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