Furnace clean and tune. Cycled system. Checked heat exchanger, found both chambers rusted and corroded. Checked, removed, and cleaned burners and flame sensor. Checked and adjusted gas pressures to maximize efficiency. Igniter tested normal, but is showing signs of being worn. Found ventor motor bearings are worn and noisy. This will cause this motor to seize and fail. Checked and tightened electrical connections and clamps. Cleared drain line. Preformed combustion test. Normal levels found in exhaust. No CO found in airstream. System is worn and future failure is expected. Job complete.