I have a Nordyne condensing gas furnace that cycles on and off while trying to reach the temperature that I set at the thermostat. For example, when the room temperature is at 62 and I increase the thermostat temperature to 68, the furnace will kick on and then it will turn off after a short while. After a couple of minutes it will kick back on and continue on and off until the room finally reaches the set temperature. The on and off cycling happens at different time intervals - it could be on for 2 minutes, off 2 minutes, on 10 minutes, off 2 minutes. I recently had the flame sensor cleaned, but no change in the cycling. I also change the filters regularly. I have a digital thermostat (White-Rodgers). I don't seem to have this cycling problem in the summer when the air conditioning is running.