Performed preventative maintenance on furnace. Discussed with customer regarding maintenance needed and any issues that I could look into for him. Customer needed some of the filters changed and he would change the rest. Changed filters out for customer. Inspected blower assembly, motor, electrical components, burners, flame sensor, ignitor, gas valve, inducer motor and overall condition of furnace and equipment in garage closet. Cleaned flame sensor and dust off the burners and components. Made sure condensation hoses were clear of build up. Checked thermostat operation, wiring, amps, temperatures and gas pressure. System is heating properly.