I find that if the brushes wear all the way out, then the motor and fuse both blow. I've had to change several motors for that reason. Whenever I try to just check the brushes, they usually still have alot of life left. I have yet to catch one before the motor goes out. Also, it's pretty annoying to take the covers of the Air Shammee and motors off to check, so that factors in to how often I do it.