The Barista Express uses volumetric buttons (1 CUP / 2 CUP) to automatically stop pouring at a preset volume. If it keeps running past that point, it's usually one of these.
01Manual mode is active
Pressing and holding a volumetric button reprograms it; a single accidental long-press can switch the machine into a state where it runs continuously until you press the button again manually. Press the same button once to stop the current pour, then do a normal single press to test if it stops correctly.
02Volume needs reprogramming
To reset a volumetric button: pull a shot manually, and press the same button again exactly when you want it to stop. This reprograms that button's target volume — worth doing periodically as your recipe changes.
03Stuck flow meter
The internal flow meter that measures poured volume can occasionally stick, particularly with mineral buildup. If reprogramming doesn't resolve it and the issue persists across both volumetric buttons, this points to a flow meter needing service — see Breville's official support page for next steps.