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Old 02-12-2011, 07:37 AM   #1
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Lennox Elite problem


This furnace is approx. 4 years old. It will not run unless the front cover plate on the furnace is either removed or not closed completely. When it is closed the burner only runs for a few seconds and then shuts down. This will happen 5 times and the control board will require a power reset. I checked the flu and the air inlet pipe. There are no obstructions. Also insured there was not water backing up in the system. Everything looks good in terms of water drainage. I think this particular unit has 2 pressure switches. Each with to pressure lines. Could one of these be going bad or is now too sensitive? I disconnected all pressure lines and insured they are also not obstructed. What to do next???????

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Old 02-12-2011, 07:48 AM   #2
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Just because your vent pipes look clear does not mean that they are. I have had it happen where Bking wrappers, plastic bags, leaves, dried up wasps nest and other debris can get sucked into the intake and partially block it. Need a very accurate low pressure manometer and special fittings on the pressure switch to see if there is enough draft and probably an experienced Lennox tech to test that. You can cut the intake pipe off by the furnace (not the exhaust) and blow from outside with a shop vac (if it has a blower feature) and see if you get good flow. I have done that several times. Then recouple the intake pipe with a 2" Fernco coupling (rubber sleeve with 2 gear clamps) from HDepot or plumbing supplier.

B4 you do that CAREFULLY and one at a time remove the pressure switch hoses one at a time so you don't mix them up, on the collector box and poke a thin drill bit or piece of wire thru those ports. They sometimes getting blocked with shmutz/sulphur deposits.

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Old 02-12-2011, 08:37 AM   #3
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Lennox Elite problem


if the furnace is a G61 or 51 or 43.... But mostly only ever saw it on the G61. Yuri is correct, Lennox had a problem with their collector box ports plugging up. Lennnox's first fix was inserts in the ports, then they came out with a new collector box design for the inside part of the ports to keep them from plugging up. I would definitely try Yuri's suggestion first before cutting the flue open.
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Old 02-12-2011, 10:42 AM   #4
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First I would like to say thanks for both responses.

checked all drain lines and there is no obstructions. Flue line and air inlet are clean. Cut into both lines and confirmed.

Could pressure switches be going bad?
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Old 02-12-2011, 11:10 AM   #5
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Does it show the pressure switch open code when this happens?
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Old 02-12-2011, 10:15 PM   #6
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you replied you checked the drain line, did you check the drain lines or the pressure ports on the collector box and the pressure hoses?
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Old 02-12-2011, 10:24 PM   #7
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At only 4 years old the parts are still under warranty but you'll have to pay a little labor to get them installed. No sense in messing with DIY IMO. Could be a faulty circuit board giving false error codes.
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Old 02-13-2011, 08:05 AM   #8
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Post the serial # and we can age it 4U.
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Old 02-20-2011, 10:40 AM   #9
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Per Yuri's message, the model number on my Lennox Elite furnace is
G51MP-48C-090-06 with SN of 5905M31099.

Problem has gotten worse. Now the burner will not stay lite with the burner cover off. It was working correctly before with the cover cracked open. Checked Flue and Air inlet pipes, no obstructions. Burner comes on for 10 sec or 2 min and shuts off. After 4-5 tries of staying lite the system shuts down. Error indicates alternating slow lights. Flame sensor has been cleaned. It looked just fine when I removed it. Still not sure why system fails. Could the two pressure sensors, may one, be going bad??
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Old 02-20-2011, 11:05 AM   #10
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CAREFULLY remove the top brown main panel above the burner box. Bend it up slightly. Then remove the aluminum cover above the burners. Then clean the face of the burner that the flame sensor sits in front of with emory paper. Give it a GOOD thorough scrubbing down to bare metal and use a mirror to verify that if you can. It gets corroded and will give you a poor flame signal and drop out the burner. You tried unplugging the ports on the collector box that the press switches attach to? Furnace was manufactured in Dec 2005. Depending on when it was installed may still be under 5 yr parts warranty.
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Old 02-20-2011, 01:34 PM   #11
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Can this brown panel be removed? There is a AC drain pipe off to the right on the top of this panel blocking my way..... I can bend it up.
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Old 02-20-2011, 02:41 PM   #12
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If you remove the 4 screws and bend it up sometimes it comes out from under the plenum. The rest of the time you have to work with it in place and suffer. If there is no way to get it out etc then you would have to remove the burners and that is a VERY difficult job and not one I would recommend you try. May want to get an experienced Lennox tech to check the flame signal and solve the problem.
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Old 02-20-2011, 05:31 PM   #13
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Unfortunantely I did have Lennox Tech over two weeks ago and he could not figure it out. He left telling me the air intake or the Flue might be plugged, nonsense. He also cracked open the front over burner cover and left. Said he was ordering pressure switches, but he still was not sure that was the prob. Stuck me with a 164 dollar bill and still I have the say problem. Wish I could find someone that really knows this system. Will Lennox even speak to me??
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Old 02-20-2011, 05:49 PM   #14
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I have worked on hundreds of that furnace and have one in my house. When pressure switches fail they stick open and very rarely have problems with the draft/vacuum on them causing them to fail on that furnace. That is why I suspect the problem has nothing to do with them. An experienced Lennox tech can check them with a manometer. I suspect your flame signal is weak and changing the airflow by opening that box etc is just getting it to hit the sensor in a different direction and boosting the signal to the minimum point. They use a fairly low signal and I cannot talk you thru testing it and you need a microamp tester. Try another company. Lennox is not responsible for poor techs anymore than any other manufacturer or car manufacturer.
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Old 02-24-2011, 11:34 AM   #15
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An analysis completed by a Lennox specialist shows the flue pipe leaving the system was cracked. Through the last 5 years water eventually made it's way to the control board and he found rust on the board. In addition, when he removed the cover behind the vent blower he found a part missing from one of the vent pipes going to the heat exchange unit. I think it is called an actuator, not sure. The inside of this black cover was burned. It appears these part was missing during install and the pipe was cracked. My builders response has been, " Your two year warranty is over". The whole system needs to be replaced......Thanks for all you previous advice.

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