After a lot of printing, the knurled wheel in the material feeder can accumulate small plastic particles. The knurled wheel can easily be taken out and cleaned in the following way.

• Remove the filament from the Ultimaker Original+
• Open up the feeder by loosening the lever and pulling out the black plastic part
• Remove the feeder bolt clip (the black clip that keeps the knurled wheel in place)

• Take out the extruder gear with the knurled wheel attached to it and simply remove the dust by blowing some air against it or using a brush
• To re-assemble the knurled wheel, reverse the previous steps