13 POINT MAINTENANCE CHECK-UP FOR 4 YR HEATING UNIT. CLEAN AND CHECK BURNERS AND BURNER OPERATION. CHECK MANIFOLD GAS PRESSURE AND FOR PROPER VENTING. CHECK THERMOSTAT, FAN CONTROL, HIGH LIMIT CONTROL, AIR FILTER, AIRFLOW, HEAT EXCHANGER, ENERGY CONSUMPTION, AND ALL ELECTRICAL CONNECTIONS. LUBRICATE ALL NECESSARY MOVING PARTS AND ADJUST BLOWER COMPONENTS. EVERYTHING IS RUNNING GREAT.