How to follow Aeropress instructions when water filters through too quickly When I try following the Aeropress instructions (2 scoops coffee, fill to level 2, stir for 10 seconds, press for 20 seconds), I find that all the water has filtered through before I get to even 10 seconds of very gentle pressing.  Most of the filtering takes place while I'm still stirring.

Am I doing something wrong?

I'm using pre-ground coffee (Tesco decaf).
It sounds as though the pre-ground coffee you are using is not ground fine enough. Generally the more coarse the grind, the faster water will filter through.   You may try throwing some additional grind on your coffee, or buy pre-ground coffee that is more finely ground (although a snob such as myself would never actually advise buying pre-ground coffee).