I have a Goodman MEC96 (GMEC960603ANAB specifically) that is having a shutoff problem. It will run once for ~15 minutes, after which it shuts off for ~1 hour before coming back on again. The status light on the board flashes red 8 times, which according to the manual means "Lockout - excessive recycles from flame proving being lost after being proven."

I have replaced the filter (with the cheap ones that allow the most airflow), I have replaced the flame sensor (the old one didn't seem to have much on it to begin with though) and I've replaced the primary limit switch, but I'm still having the issue. Air flow seems fine, and is pulling plenty of relatively cool air from the cold air return on the second floor (the furnace is on the first floor). I also stuck an endoscope as far as I could force it down the various exhaust pipes and couldn't find any blockages.

After replacing the limit switch last night it appeared to work correctly for a few hours, but then started having the same issue again. All burners appear to light up and it works fine for 15 minutes. Also flipping the breaker for the furnace off and on again makes it start right back up. The burners are all burning right up to the moment that the error happens and they shut off. From my understanding it shuts off for ~1 hour as a safety measure if it suddenly can't verify that the gas is actually burning anymore.

Could this be a circuit board issue? I'm about at my wits' end and can't figure this out, and electric heaters are only doing so much for us right now.


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