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Welcome to Just Answer, my name is Luke
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Shut power off to furnace, open cover box where the 120V wire enters the furnace, check all connections, White to white, black to black, then proper ground wire connection. restore power and check if code still there.
If still there.. shut power off again and reverse wires in same box White to black ..
restore power and try.
Hope you got system going by now, can we close question?
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Hello, This is not an answer... it is step one of what could turn out to be a many step diagnostic process.
if the error code did not go away when you reversed white and black as the previous tech suggested, then it is probably a bogus error code, or some sort of shorted wire inside the furnace... since there have been no wiring changes in the house, all this points to a bogus error code due to the printed circuit board going bad.
That said it is possible that a 120v cord cap (plug) is wired incorrectly on a new appliance in the house, that can also result in reverse polarity.
Click here for a superb video on the topic
Next step is to do a heat stress test on the printed circuit board, use a hair drier to warm it slowly and gently to 120F, if there is any chance in behavior or the error code goes away etc, the board has a micro crack in one of its circuits that expanded when the board was warmed up.
We can go from there. I am off to bed shortly and will be back at 7 am