The homeowner mentioned the furnace has high Carbon Monoxide levels. I checked over the furnace. I checked the burners, heat exchanger, inducer, blower, limit switches and wiring. I cleaned the burners and checked gas pressures and combustion air. I checked the exhaust flue. The system has Carbon Monoxide reading in the exhaust flue over 350ppm. The system will operate and then shut down on high limit. The heat exchanger has failed. The heat exchanger will need to be replaced. The chimney needs a chimney liner. The system only has return air at the furnace.
Installed new customer supplied toilet, with closet flange in main floor 1/2 bath.