When Pepper is OFF, you can press and hold the chest button until the Shoulder LEDs are blue (around 4 seconds) to perform a special start-up.
This process takes long (15 minutes), and you should not need to do this on a regular basis.
This will flash all the boards and update all the robot's firmwares. You can use this to try solve some errors.
The process is over when Pepper says “Ognak Gnuk”.