I have a Bryant 80 furnace that has worked fine for 6 seasons. Today, when we went to fire it up for the first time as winter is arriving, its flashing a "reversed polarity" light. The curious thing is that it was functioning fine previously, and we've not done any wire work or changed anything electrical in the interim.

We unplugged it and plugged in again and it fired up for a few minutes.. but it seemed reversed. There was a slight amount of heat coming out of what's usually the intake vent of our house, while the usual vents that push heat out were doing nothing. Then it turned itself off and resumed showing the reversed polarity light.

Any thoughts or suggestions much appreciated!

The first thing you need to do is to check inside your breaker panel and alert your power company. What could have happened is that the lugs holding the neutral, ground, and hot legs of power are loose. Sometimes when this happens your lights will get really bright. It can burn down your house , so you want to check this first, and look behind meter, too. There is possibly another answer : Check the polarity where power comes into furnace or at breaker box and make sure that the polarity has not been reversed.