Completed annual maintenance on one gas furnace, changed customer provided air filter 16x25x1, cleaned flame sensor, inspected igniter which looked good, inspected heat exchanger which looks good, cleared PTrap, tested blower capacitor which tested in range, all amp readings normal for inducer motor and blower motor, gas pressure readings normal, performed combustion and efficiency test which system looked normal, reset thermostat back to 73 degrees, customer renewed maintenance agreement.