Performed preventative maintenance for a Lennox system model #G61MP – 60C – 091–09, serial #5910E09876. Removed and cleaned carbon off of the flame sensor. Cleaned out the burners and burner box. Check all electrical components to ensure that they are secure and in good condition. Replaced the air filter size 16x20x1. Tested the drain line and condensate pump with several bottles of water to ensure that there are no leaks or clogs in the system. Made sure pressures switch are clear. Powered the system back on and called for heat. I observed the system starting normally and took a combustion analysis test. The inducer motor amp draw is at .23, the blower motor amp draw is at 5.2. The combustion analysis results are 11% for the o2, co is 11ppm. The system is operating properly at this time. I took a look at the nest thermostat and it is only off by 2°. In my professional opinion changing the thermostat will not fix this issue. The system is operating properly at this time.