What does 3 flashes mean on the concord 80 plus furnace how do I fix it

There should be a list of diagnostics corrosponding to the flashing led on the inside cover of one of the furnace doors. Find that and let us know what three blinks means for your specific unit. We can go from there.

If you do not find anything on the doors you should also be able to find it in the Installation & Operating Manual that came with the furnace. It may be a basic fault code though involving the pressure switch which can point to a number of other areas... let us know what you find in the literature provided to you with the furnace. Thank you.