PERFORMED A 13 POINT TUNE-UP ON HEATING SYSTEM. CLEAN AND CHECK BURNERS AND BURNER OPERATION. CHECK ALL ELECTRICAL CONNECTIONS, THERMOSTAT, AIR FILTER, HUMIDIFIER, HEAT EXCHANGER, HIGH LIMIT CONTROL. CHECK GAS PRESSURE AND FOR PROPER VENTING. ADJUST BLOWER, AND LUBRICATE ALL NECESSARY MOVING PARTS. RENEWED SA ON3 UNITS.