Performed preventative maintenance for a high efficiency Lennox furnace model #SLP98UH070V46B-2, serial #5911F04727. I powered the system down and removed the access panels. Removed and cleaned carbon off of the flame sensor and cleaned out the burners and burner box. Homeowner replaces his own air filter monthly. Filter size 16x20x1. Checked the pressure switch for clogs and tested the drain line and condensate pump with several bottles of water to ensure that there are no leaks or clogs. Checked all electrical connections to ensure that they are secure and in good condition. I powered the system back up and called for heat. Took a combustion analysis test and received the following readings, o2 is at 11.5% and the co levels are 13ppm. The inducer motor amp draw is at 7.4 and the blower motor amp draw is at 4.7. The system is operating properly at this time. The homeowner is renewing the repair agreement.