Main floor furnace: Tstac 103 F, CO 7 ppm, 9.6 O2. Changed filter. Checked condensate pump. Burners clean. Inducer fan clean. Checked dampers and purge cycle. System is functioning normally. Upstairs furnace: Tstac 128, CO 4 ppm, O2 was 14% before gas valve adjustment and 9.8 after. Changed filter, checked burners, and checked blower. Inducer working correctly. Checked dampers and condensate line. System is functioning normally.