Came out to perform preventative maintenance on furnace. Discussed with customer about maintenance, filters needing cleaned, and any concerns he may have. Customer stated that the system has been working fine so far. I pulled the electrostatic filters out and cleaned them thoroughly. Inspected blower assembly, motor, electrical components, burners, flame sensor, igniter, inducer motor, heating drains, heat exchanger, coil and overall condition of equipment. Cleaned flame sensor and dust out of the burner compartment. Made sure condensation hoses were clear. Checked thermostat operation, wiring, amps, temperatures and gas pressure. System is heating properly within manufacture specifications at this time. Customer could benefit from having the ductwork cleaned out.