Our furnace has been behaving for the last couple hours. As a result the temperature is up to 68. Other than cut the power and re-enable the power, I've done nothing to the thing. I did read up the owners manual and so I now know quite a bit more about the beast.
While poking around in the furnace room I discovered the 'slab' our house is on is cracked. The crack runs under the furnace, under the wall and into the downstairs closet. Doh.