Regarding my 12/18 post on my furnace cutting out every few days -
The problem was that the heat sensor was tripping because the furnace was working too hard. The reason? Little leaf bits in the fresh air intake. Apparently, this is a common problem. (in fact, it happened in my last house too - I wish I had remembered that before I paid someone $60 to clean them out.) Little pieces of leaves had been sucked into the intake and settled on the grate, which restricted airflow and caused the furnace to shut off.
So there you have it. Check this occasionally or else have your furnace serviced yearly.