A TUNE-UP FOR 13YR HEATING SYSTEM. CHECK HEAT EXCHANGER, HIGH LIMIT CONTROL, AIR FILTER, THERMOSTAT, GAS PRESSURE, AIRFLOW, ENERGY CONSUMPTION, HUMIDIFIER, AND ALL ELECTRICAL CONNECTIONS.. CLEAN AND CHECK BURNERS AND BURNER OPERATION. LUBRICATE ALL NECESSARY MOVING PARTS, AND ADJUST BLOWER COMPONENTS.