Performed annual heating maintenance 16 yr old Trane split downflow system closet. Nest thermostat. System operational at this time. Filter 14-25-1 x2 changed. Tested system safety features ok at this time. Blower capacitor behind panel. Hot surface ignitor ok. 90 percent furnace drain system appears to have been leaking at some point see pictures of rust inside unit. Cleaned burners and flame sensor, tested ignition process. Cleaned exterior of unit. Checked pvc flue pipe. Ran system to verify no issues, none at this time.