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  1. #1
    I have a 6 month old Lennox G51mp furnace and last night the furnace started working intermittently and the temp dropped to 60 degrees by this am. Called the service provider and he came by and said that the filter was dirty and had caused the problem. Looked and it was dirty but not that dirty...

    Later on the furnace started acting up again, turning on for short periods then off, never getting up to more then 68 degrees. Called again, wife spoke to him as I was at work and he said that because the filter had been dirty the control board had to be replaced because the 'high limit' was open and the furnace was overworked causing the control board to blow? Meanwhile, after his first visit the furnace ran fine for a while then the intermittent running again with both filters out.

    Is this plausible? I've looked at the Lennox online doc for the furnace and it doesn't mention causes of the control board failing.

    Thoughts, opinions???

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,613
    I don't know the Lennox furnace but it uses a similar board to A-S/Trane. It has had a lot of bugs in the past. One was the LED indicating open high limit when the limit was fine. Could be that your board was doing such a problem. Just a thought and could be 100% wrong.

  3. #3
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,765
    if dirty enough to be tripping limit, then limit may have gone bad. they do not like to cycle, after a while will stick open or become weak. never saw dirty filter damage board.

  4. #4
    What flash code are your diagnostic lights showing ??

    ken

  5. #5
    Join Date
    Nov 2001
    Posts
    1,874
    Originally posted by puzzled_to_ca
    he said that because the filter had been dirty the control board had to be replaced because the 'high limit' was open and the furnace was overworked causing the control board to blow?
    That sounds way off base. If anything was over worked it would be the limit. Not the control board.
    You need someone who will trouble shoot the unit till they now the problem, not change parts for some strange reason.

    Is this unit in the downflow position ?
    Meaning does the airflow come out the bottom of the unit, Or is this unit in the basement blowing the air upwards.

    If it's a downflow, depending on the unit, they are not to change the fan speed. That will cause the limit to open all the time.
    I think it's on the G51mp-36C-090 and bigger.
    It's in the book not to change the speed.

    I have replaced 3 boards since the new yr. On the 1st board the gas valve would de-energize after about 40 seconds then the unit would refire, run and repeat.
    Once in a while it would stay running.

    The other 2 times it would show fast alternating flashes.
    And the inducer motor would start and stop, about 6 to 8 times before the unit would run.

    My concern right now is, are the boards I put on made from a different stock ? or will they fail as well with the same problems.

    >>>edit... fixed post


    [Edited by jultzya on 02-21-2006 at 08:32 AM]
    If you try to fail, and succeed.
    Which have you done ?



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