Performed preventative maintenance for a Lennox furnace model #ML180UH110P48C-01, serial # 5911H10828. 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. Replaced the Merv 11 air filter size 16x25x5. Checked to ensure that the pressure switch has no clogs. Checked all electrical connections to ensure that they are secure and in good condition. Performed humidifier service for a healthy climate humidifier. Removed and replaced the old #35 water pane and installed a new one. Cleaned out the housing and drain. Tested the drain line and condensate pump with several bottles of water to to ensure that there are no leaks or clogs. I powered the system back up and called for heat. Took a combustion analysis test and received the following readings, o2 is at 10.5% and the co levels are 9 ppm. The inducer motor amp draw and blower motor amp draw are both within normal range. Tested the humidifier