Water escaping around the portafilter during a shot has a short list of causes.
The group gasket has hardened
The rubber seal inside the group head compresses to make a watertight fit. Heat and age stiffen it, and after one to three years of regular use it stops sealing.
The warning sign appears first: the portafilter handle sits further round than it used to. When new it might lock at six o’clock; after two years it goes to seven or eight.
It is a cheap part and a five-minute job with a screwdriver and something to hook the old one out.
The basket is overfilled
Too much coffee means the puck presses against the shower screen and holds the portafilter away from the gasket. A screw imprint on the used puck confirms it.
Weigh the dose and match it to the basket rating.
Not locked in far enough
Sounds obvious and happens. Some machines need a firmer turn than people expect, especially when new and the gasket is stiff.
The gasket is dirty
Coffee grounds on the sealing face stop it seating. Wipe the group and the portafilter rim before locking in — a habit worth having anyway.
Other checks
Wipe grounds off the basket rim before locking in, try a different basket in case one is cracked or warped, and brush scale off the gasket seat. In order: wipe the rim, reduce the dose by a gram, then replace the gasket.
If it leaks between shots
That is not the gasket. Look at the solenoid or the group valve.
Last reviewed 30 October 2026