1. The actual fan RPM is more than 30% above or below the fan speed RPM target.
2. Blown fuse.
1.- Vent/air intake lengths exceed the maximum allowed lengths. Refer to Section 3 - General Venting for proper lengths.
- Check for obstruction or blockage in the vent/air intake pipes or at terminations.
- Check the wiring connections at the fan and at the main control board.
- Replace the fan.
- Replace the main control board.
2. Replace fuse F2 on the control board.