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 intake and exhaust pipes and couldn't find any blockages. I've also tried directly shorted the thermostat wires for running the furnace and the issue still happens, so it doesn't seem to be a thermostat issue.
After replacing the limit switch two nights ago it appeared to work correctly for a few hours, but then started having the same issue again in the morning. Then yesterday evening it began working normally again, only to start having the same issue again this morning. All burners appear to light up and it works fine for 15 minutes every time (followed by an hour long wait before the next ignition attempt every time). Also flipping the breaker for the furnace off and on again seems to make 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.
Any ideas for what could be causing this?
Is there a gas pressure sensor in there anywhere? Can you find a schematics? That’s a goofy error code, but maybe if there’s a bad gas pressure sensor, possibly thinking there is low pressure indicating a leak. I’m mostly talking out my ass but you’re the one who came to PrepHole for advice.
Had a HEIL that was several years old that caused me some grief. The sensors in those HVAC units really are not that expensive. with the exception of the gas valve, those can cost a lot. I just replaced all of them and swapped out the control board too. Think I spent around 125 in parts and maybe an hour or two. Just take good pictures. Also, use OEM parts and not generics. Swap one a time - take pictures and understand clearly what hose or wire goes to exactly where. It's been several years and furnace still working like a champ.
It stays lit until it trips? It doesnt go out and then retry? If it isnt actuslly recycling then the control is fricked.
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15 minutes of flame is WAY to long for gas to be flowing without a light. The basic flame sensor is therefore working. The guys talking about it being a flame sensor are correct when it's just a short period. But the logic board (control board) is not going to wait 15 minutes.
That's some other timer issue on the main (control) board.
Clean the burners and make sure the flame is touching the flame sensor.
>make sure the flame is touching the flame sensor.
digits and this
The flame sensor should be directly in the flame.
With what you (OP) have described having done as a cure, if it isn't the placement of the sensor, it's likely the control board.
When I was doing property maintenance, I frequently bought good, used, working boards on eBay.
This. Jump out the sensor to rule out the sensor itself. If you still get problems it’s the control board
Clean the flame sensor, or better yet get a new one, $5.99 on Amazon. I ordered a spare.
forgot to add text:
Normal Reading but still shuts-off = Bad Ignition Control
Is the inducer fan making any weird noises when it begins its start process? Better yet do you have a gas control valve that runs directly too your controlboard with more than two wires?