Portafilter Leaking During Extraction

Symptoms

• Water seeps or drips from the top edge of the portafilter where it meets the group head during brewing
• Coffee leaks around the ears (lugs) of the portafilter rather than flowing from the spouts or basket
• The portafilter feels loose or does not lock as far to the right as it used to
• Hissing or spraying from the group head seal area under pump pressure

Likely Causes

1. Worn group head gasket. The 58 mm rubber gasket inside the group head compresses over time and no longer forms a tight seal against the portafilter rim. This is the most common cause and is a normal wear item.
2. Coffee grounds on the gasket seat. Stray grounds trapped between the portafilter rim and the group gasket prevent a clean seal. Even a single grain can cause a drip.
3. Portafilter not fully locked in. The handle should turn to approximately the 6 o’clock position (pointing directly towards you). If it stops short, the seal is not fully compressed.
4. Overfilled basket. If the coffee puck is domed above the basket rim, it presses against the shower screen and pushes the portafilter downward, breaking the gasket seal.

Step-by-step Fix

1. Clean the gasket seat. Remove the portafilter. Using a dry cloth or a dedicated group-head brush, wipe around the inside rim of the group head where the gasket sits. Remove any coffee grounds, oils, or residue. Also wipe the rim of the portafilter itself.
2. Check your dose level. After tamping, the top of the coffee puck should sit approximately 2–3 mm below the rim of the basket. If the puck is flush with or above the rim, reduce your dose by 0.5–1 g. For the 18 g precision basket, aim for 18.0 g — do not exceed 19 g.
3. Lock the portafilter firmly. Insert the portafilter into the group head and turn the handle firmly to the right until it is snug. A properly seated portafilter handle points between 5 and 6 o’clock. You should feel slight resistance from the gasket. Do not force it past 6 o’clock as this can damage the lugs.
4. Test with a blank shot. Insert the portafilter with no coffee (empty basket) and run the pump for 10 seconds. Watch for any leaking around the group head. If it leaks with no coffee, the gasket needs replacement.
5. Inspect the gasket. With the portafilter removed, look up into the group head. The rubber gasket should be smooth, pliable, and evenly seated in its groove. If it appears cracked, flattened, or hardened, replace it with a new Monverta group gasket (MV-ESP1-GASKET). Use a flat tool to lever the old gasket out, press the new one in with the flat side facing down, and run a few blank shots to seat it.
6. Check the portafilter rim. Examine the top edge of the portafilter for dents, chips, or warping. If the rim is damaged, it will not seal properly against the gasket regardless of gasket condition. A damaged portafilter should be replaced.