CLEAN AND CHECK HEATING UNIT, 20YR 9YR TAPED RETURN. CLEAN AND CHECK THERMOSTAT, AIR FILTER, HUMIDIFIER, AIRFLOW, HEAT EXCHANGER, HIGH LIMIT CONTROL, FAN CONTROL, ENERGY CONSUMPTION, AND ALL ELECTRICAL CONNECTIONS. CLEAN AND CHECK BURNERS AND BURNER OPERATION. LUBRICATE ALL NECESSARY MOVING PARTS. ADJUST BLOWER COMPONENTS. CHECK MANIFOLD GAS PRESSURE AND FOR PROPER VENTING.