Performed preventative maintenance for a Lennox furnace model #G60uhv-36b-090-07, serial #5907l02959. Powered the system down and removed the access panels. Removed and cleaned carbon off of the flame sensor, cleaned out the burners and burner box. Replaced the air filter size 16x25x5 homeowner supplied. Checked all electrical connections to ensure that they are secure and in good condition. Tested the drain line and condensate pump with several bottles of water to ensure that there are no leaks or clogs. I powered the system up and called for heat. Took a combustion analysis test and received the following readings, 02 is at 15% and the co levels are at 4ppm. The inducer amp draw is at .63 and the blower motor amp draw is at 4.2. The supply temp is at 135°F. The system is operating properly at this time.