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

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.

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Originally Posted by hvac1000

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.

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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!

I am pretty sure it is the board. Might look on Ebay.