Performed preventative maintenance on a Lennox furnace. Upon arrival I bumped the temperature on the thermostat up and watched system cycle on with a call for heat. I took a combustion analysis test and got the following: O2 is 11.3% and the CO is 9ppm. I took amp readings on the inducer motor and blower motor, both are in good range. Checked and cleaned the flame sensor of any carbon build up. Checked all electrical components to ensure the connections are good and tight. I also checked the drain line to confirm that there are no clogs. Checked operation of pressure switches. Checked and swept out burner box of all debris. Watched system cycle off when temperature was reached. Returned thermostat to homeowners desired temperature. System is operating properly at this time. Model # Sl280uH090v36B Serial # 5914F31297