Today we performed one system furnace tune up on trane 60k furnace. Cleaned flame sensor, fuel rail and inducer port. Inspected heat exchanger with digital camera found failed heat exchanger @ 7 o clock tagged furnace unsafe due to potential carbon monoxide fumes. Checked gas pressures, inspected ductwork and cycled equipment from thermostat. Gave client repair option and scheduled install supervisor to give options on updating furnace left all equipment in service