1ST CLEAN AND CHECK FOR 11YR HEATING SYSTEM. CLEAN AND CHECK BURNERS AND BURNER OPERATION. ADJUST BLOWER COMPONENTS, AND LUBRICATE ALL NECESSARY MOVING PARTS. CHECK THERMOSTAT, AIR FILTER, AIRFLOW, ENERGY CONSUMPTION, HEAT EXCHANGER, HIGH LIMIT CONTROL, GAS PRESSURE, HUMIDIFIER, AND FAN CONTROL.