Sometimes, when our 1997 furnace comes on, you can hear the flame "whoosh" and keep going for maybe 10 seconds, but the fan doesn't start up then. It tries again - and if all three times don't work, the furnace automatically shuts off for several hours. Lately this has been happening more than once a day - it's cold and the furnace has to come on a lot.
Any idea what this could be? We are hoping we don't have to replace the furnace yet!