I have a Day & Night furnace model #80U-19, it has a Honeywell Fan limit switch model #L4064A1628. The regulator was replaced last winter & the furnace worked fine for the rest of the season. We left the pilot on over the spring, summer & fall months of 2010. I checked to make sure the pilot was still burning, which it was, I then turned the thermostat up to about 75 degrees. I heard the thermostat click, but nothing happened at the furnace. We tried a couple more times with my wife operating the thermostat control while I was standing at the furnace. Each time the thermostat was adjusted until it clicked on the burners would start but then immediately go out. They wouldn't stay lit for more than a second or two. Not sure where the problem lies. Any suggestions?