Performed preventative maintenance for a high efficiency Lennox furnace model #G61MP-60C-111-09, serial #5909M11891. Upon arrival the system was heating the home. I took a combustion analysis test and received the following readings, o2 is 12.7% and the co levels are 9ppm. The supply temp is . The inducer motor amp draw is at .30 and the blower motor is at 6.1. I powered the system down and removed and cleaned carbon off of the flame sensor. Cleaned out the burners and burner box. Replaced the homeowner supplied 201 air filter. Checked the pressure switch for clogs and checked all electrical connections to ensure that they are secure and in good condition. Cleaned out the trap and tested the drain line and condensate pump with several bottles of water to ensure that there are no leaks or clogs.