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Old 02-21-2012, 10:27 AM   #1
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Lennox furnace won't stay lit.


I have a Lennox furnace that won't stay lite what happens is it lites for a minute or two then cuts out it does this 4 to 5 times. The led lights flash slowly at different times and the chart reads the burner failed to ignite. I have cleaned the flame sensor, checked for blockage in the tubes and the ignitor and bypass the thermostat and nothing is making a difference. Any suggestions.

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Old 02-21-2012, 10:53 AM   #2
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Lennox furnace won't stay lit.


post the complete model #.

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Old 02-21-2012, 10:57 AM   #3
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Lennox furnace won't stay lit.


if you have a multimeter that reads dc millivolts, i would touch the flame sensor male plug and its wire female, sould read 12 millivolts dc plus or minus 1-2, while its going through the sequence of operation, anything around 3-9 should be changed hope that helps
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Old 02-21-2012, 12:50 PM   #4
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Lennox furnace won't stay lit.


Between 2 and 5 micro amps is what want to see. It's not a milli volt system
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Old 02-21-2012, 07:13 PM   #5
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Lennox furnace won't stay lit.


thanks for the correction Marty, i jumped the gun on the micro amp range, was thinking luxaire
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Old 02-22-2012, 06:14 AM   #6
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Lennox furnace won't stay lit.


Don't sweat it. Too many furnaces out there to remember them all.
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Old 02-23-2012, 09:55 PM   #7
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Lennox furnace won't stay lit.


I'm having the same exact problem. The LED's are flashing slowly alternately on my Lennox Elite G51 furnace which it shows could be one of 4 things. I've cleaned the flame sensor checked the tubes for clogs on the pressure sensors and check the electrical connections.

I've tried to get a reading on the flame sensor as stated above but my sensor only has the one wire going to it so I'm guessing that I should put the other contact on a ground somewhere. I did that and I'm getting around 17 volts with the furnace in the running state.

Another thing that I'm thinking it might be is the previous home owners seem to have taken the burner cover plate off and thrown it away. I just noticed that it had screws that weren't holding anything the other day so I found a drawing and sure enough there should be a cover plate on it. But it has been this way for the past 3 years since we've owned the house so I'm guessing that isn't causing my issue.

So if it is a bad flame sensor then where can I get one? I've searched all over the web for parts (trying to find the burner cover) and can't find anything for the Lennox Elite G51 furnace.

Any help would be greatly appreciated.
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Old 02-24-2012, 06:14 AM   #8
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Lennox furnace won't stay lit.


you need that cover plate or the furnace may overfire and get damaged as the gas valve won't modulate properly. it needs to sense the pressure in the burner box and w/o the cover won't get a proper reading. cozyparts.com may be able to special order it but you need to phone them and describe it as it will be special order and may take a few weeks to get. what is that code saying. you need to put your meter in series with that wire and where it attaches to the circuit board. you may have an venting obstruction on the intake and they took the cover off to cheat and take air from the house.
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Old 02-24-2012, 08:10 AM   #9
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Lennox furnace won't stay lit.


Thanks yuri. The options for the slow flashing alternating LED codes are all watchguard errors and they are:
A. Burners failed to ignite
or
B. Limit open more than 3 minutes
or
C. Lost flame sense more than 5 times in one heating cycle
or
D. Pressure switch opened 5 times in one heating cycle

Seems to be somewhat erratic. It will run for a couple days and then fall all over itself for a couple of hours and then will run again out of the blue without me doing anything to it other than opening the access panel.
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Old 02-24-2012, 08:30 AM   #10
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Lennox furnace won't stay lit.


Get a cover for it and then we can go from there. Won't have a proper flame w/o it.
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Old 02-24-2012, 10:44 AM   #11
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Lennox furnace won't stay lit.


OK so I called and that stupid thing is $152 so is there any way that I can make a makeshift one to test it out before I shell out that kind of money for a little piece of sheet metal?

Or are there any used parts places that you know of that I might be able to try?
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Old 02-24-2012, 11:33 AM   #12
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Lennox furnace won't stay lit.


It is not just a cheap piece of metal, it has a heat resistant silicone gasket and a viewing window. w/o the gasket the burner will pulsate. no used ones that I know off.
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Old 02-24-2012, 04:50 PM   #13
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Lennox furnace won't stay lit.


I do sheet metal work and u can have it made up, and a bead of silicone should replace gasket.

But the cost to make it and install it would be more in the $250 range..I would buy the OEM part because it's going to cost you more in grief and money if you don't/
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Old 03-07-2012, 11:07 AM   #14
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Lennox furnace won't stay lit.


OK so I received the burner box cover and installed it and now the furnace won't run at all. I think I know why the previous home owner to the other one off. It doesn't seem to be getting enough air and the flame cuts out. We have about 6 feet of 2 1/2" PVC going from the furnace and then it goes to 3" and there is about 20 feet of the 3" PVC to make it outside. There are roughly 4 or 5 90 degree elbows in the mix to make it outside.
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Old 03-07-2012, 02:56 PM   #15
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Lennox furnace won't stay lit.


When you say the furnace won't run at all with the cover on, how far does it go in the heating attempt and what code do you now get with the door in place when it locks out?

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