Full Speed Upon Power Up

This condition is when the treadmill goes to full speed as soon as you power up the treadmill. Typically when this occurs, it is an indication of a short circuit in the Treadmill Motor Control Board

Be sure to test the motor for a short-to-ground condition. If a motor shorts completely, it can cause a controller to short circuit and have a runaway condition like this.
Be sure to test the other electrical part to confirm they do not have a short-to-ground condition.

Even if your treadmill runs away only one time and then returns to normal operation, we suggest replacing the motor control immediately because it is a dangerous proposition when this malfunction occurs and has been show to have quick recurrence with the same controller.