This morning I noticed it again: Setting the thermostat to 68 with
my house at 63 degrees, the 18-year old Day-and-Night fired up
beautifully, ran about five minutes, and then turned off the flame
and soon afterwards the blower. Before the blower stopped the
gas pilot had already ignited to resume. Three or four such short
cycles ensued. Then -- miraculously -- the furnace stayed
on for a full 45 minutes (it's still running) without interruption.
I'm sure this is an easy diagnosis for any gas furnace guru.
Please share your thoughts!