Complete heating maintenance in Atlanta, find Trane gas furnace operating with weak flame sensor and incomplete combustion, causing high CO level. Complete combustion calibration service and replace flame sensor for 18 year old Trane system. System operating with worn ignition, damage water safety and missing cover for condensation pump. Note: master bedroom not comfortable due to long duct run. Suggest to run direct 10†supply run and drop down to 8†to help improve airflow.