I'm replacing it because it has 2 cracked heat exchangers. This was
discovered when a repairman was out to replace the igniter that had
gone out. He ordered us not to run the furnace, but it's cold! I'm
aware of the risks and have a working CO monitor in the house. Even if
I could replace the heat exchangers under warranty (which I can't) I
feel that this is a sign of things to come, so the furnace must be
replaced.