There are a couple of key points to keep in mind:
1. The GriGri must be loaded properly in order to function correctly. Thankfully there are diagrams on the unit for you to refer to when you load up the climbers rope. Read the literature that comes with the device.
Petzl’s website is a great resource for instructional videos and downloads of the owners manual.
Petzl’s Gri Gri Short Video