A furnace requires several routine maintenance tasks to keep it running efficiently and safely. Every 1-3 months, air filters must be replaced to prevent air restriction. Other pre-inspection tasks include ensuring the thermostat is functioning properly, cleaning the blower assembly, and cleaning the motor. If the pilot system is not working properly, the furnace will not work properly; thus, it (and the ignition system, if so equipped) must be inspected, as well as the burner assembly. If the furnace has moving parts, ensure all parts are properly lubricated. Also, make sure any and all electrical connections are secure. Finally, inspect the heat exchanger for cracks and the flue for leaks before reassembling everything and covering your tracks.