Did a preventative maintenance on a gas furnace. Cleaned flame sensor. Did a combustion test and the Ppm was 65 and o2 was 15. Also did an amp check on the inducer motor and blower motor which both met the furnace specs. And I cleaned out the blower mood or housing and the burner rack. Changed out to 14 x 25 x 1 filter. Checked ohms the hot surface igniter. System is operating properly at this point. M#ML180UHO45P24A-55 s#1716H17031