My furnace is about 4 or 5 years old. I recently noticed that it will go into a stage where the thermostat is requesting heat, but the furnace goes through this "cyling" routine. It will burn for 10 seconds, go out for 50 seconds, light up again for 10 seconds, go out for 50 seconds.... This will occur for 5 cycles and then shut down. Do I need a new thermocouple to confirm that the flame is on? It seems that it will not completely fail, because it eventually fires and keeps the house within a degree of the thermostat setting. Possibly the cycling is an energy saving feature that I never notice before.