If water is escaping around your portafilter instead of going through the coffee, the cause is almost certainly one of three things, and in this order: coffee grounds on the rim of the basket or the group, too much coffee in the basket, or a group gasket that is dirty, hardened or worn. All three are cheap or free to fix and none of them means the machine is broken. Wipe the rim, drop your dose by a gram or two, and clean the gasket and shower screen — that resolves the large majority of leaks. The first thing to do, before anything else, is to look at the puck.
A leak is a seal failure, and the seal is simple: the lip of the basket presses up into a rubber or silicone gasket in the group head, and the portafilter's lugs hold it there under nine bars of pressure. Anything that sits between the basket lip and the gasket — grounds, old coffee oil, a swollen puck — breaks the seal and water takes the easy route sideways. Anything that stops the handle rotating far enough does the same. Nine bars is a lot of pressure looking for a way out, and it will find whichever route is weakest.
Diagnose it with one shot.Lock the portafilter in without any coffee at all and run the pump for five seconds. If water still escapes around the group, the problem is the gasket or the lock — the coffee was never the issue. If it seals perfectly dry, the problem is your dose, your distribution or the grounds on the rim. That one test splits the whole diagnosis in half, and it takes ten seconds.
Then work through the five causes below in order. They are ranked by how often they are actually responsible on home machines, not by how dramatic they sound. Note that one cause — a leak during the pre-infusion or at the very end of the shot only — is often normal behaviour on a three-way-valve machine rather than a fault at all.
A leak that is specifically spraying rather than seeping, or that comes with a sour, fast shot, is a different problem: that is channeling through the puck, not a seal failure. See how to fix channeling. And if the machine is leaking from underneath rather than around the group, that is a drip tray, hose or boiler issue, and it is not what this page is about.
The five causes, in order of likelihood
1. Grounds on the basket rim or the gasket. The most common cause by a wide margin, and the easiest to miss because the grounds are the same colour as the gasket. After dosing, wipe the top edge of the basket and the rim of the portafilter with a fingertip or a cloth before you lock in. If you grind directly into the basket, this will happen every single time unless you use a dosing funnel.
2. Too much coffee in the basket.An overdosed puck swells when it is wetted and presses up into the shower screen, which lifts the basket lip away from the gasket. The classic tell is a puck with a deep circular imprint of the shower screen in it, or a puck that sticks to the screen when you unlock. Drop the dose by one to two grams and see if the leak stops. This is especially common on 54mm Breville and 51mm De'Longhi baskets, where people apply 18-20g doses written for 58mm commercial baskets.
3. A dirty, hardened or worn group gasket.Gaskets are rubber or silicone and they absorb coffee oil, harden and eventually compress permanently. A gasket caked in old coffee cannot form a seal even when nothing else is wrong. Clean it with a group brush and a backflush detergent; if the rubber is cracked, glazed or visibly flattened, replace it — it is a consumable, typically replaced every 6-12 months on a daily-use machine, and it is one of the cheapest parts on the machine.
4. The wrong basket, or a basket that does not seat.A basket that is the wrong diameter or the wrong depth will not present its lip to the gasket correctly. This bites people who buy "58mm" parts for a 58.5mm machine, 54mm parts for a 53mm Ninja, or aftermarket baskets for a De'Longhi Dedica whose stock portafilter carries a plastic insert. Confirm your size in the portafilter size chart by brand and check the fit notes on the matching accessories page.
5. The handle is not rotated far enough.On a new machine the gasket is stiff and the handle should come to a firm stop around the 6 o'clock to 7 o'clock position — if yours stops well short and feels loose, you are not engaging the lugs fully. On an old machine the opposite happens: a compressed gasket lets the handle rotate much further than it used to, which is itself a sign the gasket is due for replacement.
Diagnosis table: what the symptom tells you
| What you see | Most likely cause | Fix |
|---|
| Leaks with an empty basket locked in | Gasket dirty, hardened or worn; or handle not locking | Clean the gasket; replace it if cracked or flattened |
| Shower-screen imprint in the puck, or puck sticks to the screen | Overdosed basket | Reduce dose by 1-2g |
| Grounds visible on the rim after unlocking | Grounds breaking the seal | Wipe the rim; use a dosing funnel |
| Handle rotates much further than it used to | Gasket compressed with age | Replace the gasket (a 6-12 month consumable) |
| Handle stops short and feels loose | Not fully engaged, or wrong basket seating high | Rotate firmly to the stop; confirm basket size and depth |
| Spraying sideways with a fast, sour shot | Channeling, not a seal failure | See how to fix channeling |
| A few drips during pre-infusion or right after the shot | Often normal three-way-valve behaviour | Nothing — this is the machine releasing pressure |
How to clean a group gasket properly
Turn the machine off and let the group cool enough to touch. Remove the portafilter and look up into the group: you should see a flat rubber or silicone ring with a shower screen inside it. Run the group brush around the gasket groove while flushing short bursts of water, which carries the loosened grounds out rather than deeper in. If the machine has a three-way valve, backflush with a blind basket and a cleaning tablet. Then wipe the gasket face and check it: supple and matte is healthy; glazed, cracked or permanently dished means replace. On most home machines the gasket is a push-fit part you can lever out with a screwdriver and replace in a few minutes, and it costs very little.
Dose by basket size, not by internet advice
Overdosing is the second most common cause of leaks and the easiest to create by accident, because almost all espresso advice online is written for 58mm commercial baskets. Use the numbers for your actual size — roughly 18-20g at 58mm, 18-19g in a 54mm Breville basket, 14-16g in a 51mm De'Longhi basket — and if in doubt, go down a gram. A dry puck should sit a few millimetres below the basket rim before brewing, with enough headroom that it can swell without touching the shower screen. Portafilter sizes explained covers how the sizes differ, and espresso puck prep covers the dosing routine.
When it is actually a fault
Three cases justify a service call rather than a wipe and a dose change. A leak that continues after a thorough clean and a brand-new gasket points at a damaged group seat or a deformed basket lip. Water appearing from the body of the machine rather than the group is a hose, boiler or over-pressure-valve issue. And a leak accompanied by weak pressure and poor flow is usually limescale restricting the water path, which is a descaling job rather than a sealing one — see how to descale and espresso pressure problems.
