Water escaping around the rim of the portafilter rather than through the coffee has a few causes.
The group gasket
The rubber seal in the group head that the portafilter presses against. It hardens and shrinks with heat and age.
Symptoms: the portafilter handle sits further right than it used to, and water weeps from the edge.
Replace it annually. It costs very little and it is the answer most of the time.
Too much coffee
An over-dosed basket holds the portafilter away from the gasket, so it cannot seal.
Test: tamp, insert, remove. A deep imprint from the shower screen on the puck means the dose is too high.
Coffee grounds on the rim
Grounds on the basket rim or the gasket break the seal. Wipe the rim before locking in.
Not locked in far enough
The portafilter should engage firmly. If the gasket is new, it may sit further left than you are used to.
A cracked or warped basket
Uncommon, and it happens. Try a different basket.
Scale on the gasket seat
Descale, and clean the group with a brush.
If it leaks when idle
That is different — a leaking solenoid valve or a failing check valve, and it needs service.
The order
Wipe the rim, reduce the dose by a gram, then replace the gasket. In that order, it is nearly always solved.
Last reviewed 8 August 2026