Performed level 2 furnace cleaning. Burners and flame sensor are clean. Heat exchanger looks good. Gas and exhaust levels are normal. No CO detected in the air. Drain is clear. Heat rise was 42 degrees. We will need to come back and perform a combustion analysis again. I had high CO readings in the exhaust. The air test was okay, but I think it would be in best interest for the customer if we ran another analysis to be safe.