MAINTENANCE TUNE-UP FOR HT UNIT 27 YR. FOUND US ON HEIL WEBSITE. CLEAN AND CHECK BURNERS AND BURNER OPERATION. CHECK MANIFOLD GAS PRESSURE AND FOR PROPER VENTING. CHECK THERMOSTAT, AIRFLOW, AIR FILTER, FAN CONTRO, HIGH LIMIT CONTROL, HEAT EXCHANGER, ENERGY CONSUMPTION, AND ALL ELECTRICAL CONNECTIONS. LUBRICATE ALL NECESSARY MOVING PARTS AND ADJUST BLOWER COMPONENTS. EVERYTHING IS RUNNING GOOD.