We noticed this problem with our furnace in the last week or so, and we thought maybe our thermostat was malfunctioning, so we went and put a new one in, but the problem still persists. What happens is the furnace will run like it normally does for an hour or two, then it will just stop turning on. The thermostat is a digital, and it indicates whether the furnace should be on or not. Well, after the aformentioned time period, the thermostat will indicate the furnace should be on, but it isnt. In that time the temp starts to drop, and it still wont turn on.
Sometimes turning off the thermostat and then turning it on works, but then that usually wont work either. I found if I switch the power off and on on the furnace itself, it starts working again. Any ideas?