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    ST111's Avatar
    ST111 Posts: 2, Reputation: 1
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    #1

    Nov 9, 2008, 09:58 PM
    Lennox furnace won't ignite
    Lennox mod GZ4m3/4-120A-4 Ser 6395M52686 12/95

    Board LED shows firing sequence, Gas valve opens, igniter doesn't spark, gas valve closes approx 8 sec. later then retries twice more. The furnace can be ignited with lighter during this sequence and appears to burn normally for approx 8 min. then burner shuts off for several, after which ignition sequence attempts again. Limit switch circuit appears closed (continuity, voltage present), R/O, high limit, airflow all seem OK but spark never generated. Is this a board problem, or am I missing something stupid?

    Thanks
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Nov 9, 2008, 10:47 PM
    If the spark is not being generated then it probably is a problem with the spark pack or circuit board if the spark is generated by the circuit board itself. Make sure the spark cable and connections are good.
    ST111's Avatar
    ST111 Posts: 2, Reputation: 1
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    #3

    Nov 10, 2008, 09:54 AM
    Quote Originally Posted by hvac1000 View Post
    If the spark is not being generated then it probably is a problem with the spark pack or circuit board if the spark is generated by the circuit board itself. Make sure the spark cable and connections are good.
    Thanks! No spark generated, I think, but can I find spark voltage with a VOM? Is it high voltage DC? It comes from a generator on the board, a approx 1" blue cylinder. These people can't afford a new board and I've rung out the resistors and seem to have found several open, but I hesitate to go desoldering unless it's a last resort. Thanks again for the expert advice. Love the avitar!
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #4

    Nov 10, 2008, 11:29 AM
    I am pretty sure it is the board. Might look on Ebay.
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