Help Lennox furnace

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Old 09-28-12, 11:35 AM
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Question Help Lennox furnace

I am having the same problem which appeared suddenly after years of working properly (ie: burners light for a few seconds then stop) only it is with the blower door. I have removed the filter (it was quite dirty and restrictive) but problem persists. Note that there is a fairly strong vacuum when I put the blower door in place with no filter. The vaccuum strength was much stronger with my dirty filter in place. Furnace runs fine if if I prop the door open slightly with a stick thereby removing the negative pressure in the blower compartment. Could be a problem with the pressure switch? Maybe an air flow problem but nothing has changed in ventilation that I can see aside from my filter. Lennox 80UHG3/4. Appreciate any help. Thx
 
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Old 09-29-12, 01:28 AM
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Please don't revive an old thread. Start a new one.


Take the cover off the burner compartment of the furnace.

Observe the sequence of events that occurs at the furnace when you turn up the thermostat and post that sequence of events in order and in detail.
 
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Old 09-29-12, 04:12 AM
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New thread started...................
 
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Old 09-29-12, 06:00 AM
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Did it work fine when you place a new filter in place? Also, what style are you using?
 
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Old 10-03-12, 09:45 AM
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Furnace won't stay lit unless blower door open.

Sorry, didn't know the forum protocol.
A little more background. Dec 2010 a furnace tech determined that the circuit board needed replacement ($650). I was out of work and am still financially challenged. He did an inexpensive rewire that bypassed the circuit board and supplied power to the blower constantly, apparently an OK approach that he claimed would be easier on the blower (no stopping/starting) and better air circulation in the house. Furnace worked great after that until recently. I discovered that it worked fine if the blower door was opened (relieving the vacuum in the blower compartment and/or increasing airflow available to the blower)

Jay11J: I removed the filter completely to remove any possible intake restriction. Definitely this was an issue. When I removed the filter it sounded like the furnace was straining less but the lighting problem persisted. Will be using a different filter going forward.

Seattle Pioneer: The upper fan starts, the element glows bright orange then the gas kicks in and nice blue flame for a 5-7 seconds then stops.

FYI, today woke up cold with the furnace not staying lit even with the blower door propped open. I sanded the flame sensor and now it is working again, even with the blower door closed. (???) I think it was a combination of restrictive filter and dirty flame sensor.

I still have a few questions: Is there supposed to be negative pressure in the blower compartment (there still is). Also, do you feel the band-aid solution described above is safe and sustainable. We don't mind the blower on constantly.

Thanks for taking time with my questions.
 
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