Did you happen to receive an “error 2: open Roomba’s brush cage and clean brushes” from your Roomba?  Naturally, you checked the brush cage and the extractor brushes.  To your surprise, there was nothing you can see that could have jammed the brushes.  This exact situation happened to me and the solution was quite simple to fix.

Reason:  I was using aftermarket/3rd party extractor brushes

Solution: Purchase genuine Roomba extractor brushes

After I installed the genuine brushes, the error code went away.  You’re probably thinking, is there any way I can still use the 3rd party brushes since I can’t return them?  Here’s a hack for you, since you need the two brushes (black and white one) to work together.  You can use one 3rd party brush and one genuine brush.  This worked for me but your mileage may vary.  If this solution works for you, be sure to check the brushes periodically to ensure both brushes are degrading at the same rate.  From my experience, my 3rd party brushes degraded a lot quicker than the genuine brushes offered by iRobot.  I can definitively say the genuine iRobot brushes are durable and usually last beyond the recommended time frame of 6 months, but I also believe it all depends on what types of flooring you have.  The bristles on my 3rd party brushes were all flat in 3 months.  Moral of the story, you get what you pay for.  For an in-depth review of the Roomba Genuine 800, 900 Series Extractor Brush, you can watch my video below: