Depends if you are by it when it quits.You would here the fan running if it is working
fire needs air. Air comes from the fan. I also lean towards a fan problem. To the great list above I'd add intermittent wiring...I'd particularly inspect and twiddle with the connections. In other words, the fan may be ok, and the controller ok, they just might not be communicating to each other.Depends if you are by it when it quits.
Fans don't always just quit.
They can get hot and slow down or stop.
Once cooled down they can starts again.
Eventually they will die completely.