Came out to perform preventative maintenance on furnace. Discussed with customer about maintenance being provided, filters, and any issues. Customer stated that the filter may need to be replaced, but other than that, the system is working fine. Inspected blower assembly, motor, electrical components, burners, flame sensor, ignitor, gas valve, inducer motor and overall condition of equipment. Blower wheel has slight dust build up on it. Heat exchanger checked out. Cleaned flame sensor and dust off burners. Tested thermostat operation, wiring, amps, temperatures and pressures. Cycled unit multiple times to ensure everything is working. System is heating properly at this time. Customer would benefit from more insulation added into his attic.