Grinder wont grind after cleaning - By Dave Corbey
This mainly applies to the high end flat burr grinders such as the Macap M4, Mazzer Mini, etc.. When the burr carrier is removed for cleaning, many people adjust it back to the "touching point" just where the flats of the burrs touch, then back off a bit for espresso. The trouble is that people don't clean their grinders very often (no problem with that), so they forget where the burrs should be and can sometimes have them far too close. This causes the beans to popcorn about, but they don't feed through and the grinder won't grind anything. If this happens to you, simply back the grind off to a coarse French press, check the beans are feeding through and then tighten the grind progressively down to espresso.
The main clue that this is the problem is when it happens directly after cleaning the grinder.