Did a preventive maintenance on a gas furnace. During the maintenance I clean the flame sensor check the hot surface igniter. Cleaned out the burner box and the blower motor housing. Also did an amp check on the inducer motor and the blower motor which both meet the furnace specs. And tightened and made sure all electrical connections were secure. Did a humidifier maintenance as well during the maintenance I switched out the number 35 panel and wipe down the whole entire humidifier then made sure it was working properly and draining then I made sure that the condensate pumping was working properly which it was. Did a combustion test the parts per million were 22 and the O2 was nine. System is operating properly at this point. M#TG8S080B12MP11 s#W1N7386172 changed out 16 x 25 x 1 filter.