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Old 02-07-2011, 09:58 PM   #16
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Lennox Furnace burner won't stay on


Clean the face of the burner that the sensor sits in front of with emory paper. It has to conduct the flame signal from the sensor which gets converted to DC current thru flame rectification. If that burner is even slightly corroded or rusty it weakens the signal. Make sure the ground wire from the burners on the right is tight and not corroded if it has one.

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Old 02-08-2011, 08:25 PM   #17
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Lennox Furnace burner won't stay on


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Originally Posted by yuri View Post
Clean the face of the burner that the sensor sits in front of with emory paper. It has to conduct the flame signal from the sensor which gets converted to DC current thru flame rectification. If that burner is even slightly corroded or rusty it weakens the signal. Make sure the ground wire from the burners on the right is tight and not corroded if it has one.

I cleaned it today using the emory paper. It was some what dirty but I cleaned it well. This is a 7 year old unit. I put everything back in order and STILL the same problem

I'm starting to think maybe the circuit board is bad or what??????
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Old 02-08-2011, 08:48 PM   #18
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Lennox Furnace burner won't stay on


There could be many problems. The pressure switch could be dropping out the gas valve could be dropping out and you should check your flame signal with a meter. Has anything been done to the venting inside or out. Is anything in the venting?
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Old 02-08-2011, 08:51 PM   #19
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Lennox Furnace burner won't stay on


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Originally Posted by marchvac View Post
There could be many problems. The pressure switch could be dropping out the gas valve could be dropping out and you should check your flame signal with a meter. Has anything been done to the venting inside or out. Is anything in the venting?

There have been no changes to the venting. As far as I know, I don't believe there is anything in the venting...
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Old 02-08-2011, 08:55 PM   #20
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Lennox Furnace burner won't stay on


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Originally Posted by echo6romeo View Post
There have been no changes to the venting. As far as I know, I don't believe there is anything in the venting...


The LEDs are both flashing fast= normal operation, but the burners keep going through the same cycle of only staying on for about 3 seconds... The fans are working fine. Its about 67 degrees inside, and I have the thermostat set to 80.
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Old 02-08-2011, 09:07 PM   #21
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Lennox Furnace burner won't stay on


before you condemn the board you should get a votmeter and check the pressure switch, gas valve and limits. It could also be the thermostat. You would have to disconect the wires from w and r and jump them out.

Last edited by marchvac; 02-08-2011 at 09:12 PM.
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Old 02-08-2011, 09:15 PM   #22
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Lennox Furnace burner won't stay on


Why did you change the igniter? Where did you get it from? There are several versions of that igniter and they have to match the model AND series of that furnace and circuit board. Hope you got the right one. Universal igniters DO NOT work with Lennox units as Lennox uses a reduced voltage system for them. Marchvac is heading you in the right direction.
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Old 02-08-2011, 09:18 PM   #23
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Lennox Furnace burner won't stay on


Hey Yuri long time how is things. I had to do a job in regina last fall
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Old 02-08-2011, 09:27 PM   #24
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Lennox Furnace burner won't stay on


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Hey Yuri long time how is things. I had to do a job in regina last fall

I purchased the igniter because I thought that may be the problem which wasn't. It's not the Lennox original part but looks pretty close. Either way, when I installed it, nothing changed and it still ignites the burners like the other one did. Now the flame sensor I purchased from Cozyparts and its the original part. I do have a volt meter (not digital) but not sure how to test the pressure switch, gas valve and limits...
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Old 02-08-2011, 09:32 PM   #25
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Lennox Furnace burner won't stay on


Here's my meter.
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Old 02-08-2011, 09:34 PM   #26
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Lennox Furnace burner won't stay on


After the furnace lights the pressure switch should stay closed which means you should have no voltage across the two terminals. If the gas valve has 24v and shuts off then the valve is bad. But it could also be the thermostat.
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Old 02-08-2011, 09:37 PM   #27
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Lennox Furnace burner won't stay on


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Originally Posted by echo6romeo
Here's my meter.
I'm not even sure if this type of meter will work.
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Old 02-08-2011, 10:33 PM   #28
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Lennox Furnace burner won't stay on


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Originally Posted by marchvac
After the furnace lights the pressure switch should stay closed which means you should have no voltage across the two terminals. If the gas valve has 24v and shuts off then the valve is bad. But it could also be the thermostat.
Can you please explain how to check the pressure switch with the volt meter (I'm new to the volt meter and the furnace).

Also, just an update, the unit has been running for several hours now since I reset it to clean the burners. The fan is always running, the LEDs are displaying normal operation, the igniter is igniting the burners which will burn for 3 seconds before turning off. This process of trying to keep the burners on for more then 3 seconds keeps repeating after about every 20 seconds of rest/ burners off. Still no lock out mode.
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Old 02-08-2011, 10:39 PM   #29
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Lennox Furnace burner won't stay on


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Originally Posted by echo6romeo

Can you please explain how to check the pressure switch with the volt meter (I'm new to the volt meter and the furnace).

Also, just an update, the unit has been running for several hours now since I reset it to clean the burners. The fan is always running, the LEDs are displaying normal operation, the igniter is igniting the burners which will burn for 3 seconds before turning off. This process of trying to keep the burners on for more then 3 seconds keeps repeating after about every 20 seconds of rest/ burners off. Still no lock out mode.
This is a picture of my unit:
Lennox G43UF -36b-070-08
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Old 02-11-2011, 11:01 AM   #30
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Lennox Furnace burner won't stay on


Quote:
Originally Posted by echo6romeo

This is a picture of my unit:
Lennox G43UF -36b-070-08
It's FIXED!! I just unplugged the red tube from the pressure switch and blew in it to clear it. That's it.

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