Performed preventative maintenance on furnace for customer. Changed out filter in home. Inspected the blower assembly, motor, electrical components, heat exchanger, burners, flame sensor, igniter, inducer motor and overall condition of equipment. Heat exchanger has no failures seen at this time. I cleaned the flame sensor and brushed dust off the burners. Checked furnace operation, wiring, amps, temperatures and gas pressure. System is aging and customer is aware, but it is still operating properly at this time.