When the fan in my Outfitter quit, it was the safety switch that shuts off the fan when you close the roof hatch. Basically, what AnEv942
says.
It was only 2 or 3 years old at the time.
The quick and dirty solution for me was to bypass the safety switch.
Edit: I think, the switch in question is in the picture on the lower left. Our fan had no automatic controls, so bypassing the switch wasn't a risk. When I close the hatch, I am next to the fan and can turn it off, there was no risk of it running inadvertently when no one is present. This may be different for the OP's version of the Fantastic Fan.