Group Gaskets and Shower Screens

The short answer: on a commercial machine in daily use, plan to replace the group head gasket every 3 to 6 months. Change the shower screen when the holes are blocked, the screen is bent, or coffee oil will not clean off it. A busy group, or one that runs hot from open to close, will hit the short end of that gasket interval. Both parts are front-end work. They are checked and changed as part of preventative servicing, not left until the group is wet.

What each part is doing

The gasket is the seal the portafilter locks against. When it hardens or cracks, the seal goes and water finds a way out around the ears instead of through the coffee. The shower screen sits above the puck and spreads the water from the group. If the holes clog, the water hits the coffee in a jet rather than a sheet, and the shot channels.

How to tell they are due

The portafilter will not sit. It locks past its usual stop, or you have to heave it round to get a seal. That is a tired gasket, not a technique problem.
The group weeps. Water or wet coffee grounds around the lugs during a shot. Staff start holding a cloth there without thinking about it.
Shots go uneven. One side of the puck is wetter, blonding starts early, and dialling in no longer fixes it. Look at the screen before you blame the coffee.
The screen will not come clean. Backflushing should clear it. If the holes stay dark, or the screen is domed or split, it is finished.

Why this is a service job, not a rescue

A gasket and a screen are small parts, and they fail in a way that looks like a coffee problem. Replacing them is ordinary front-end servicing. On a preventative visit we change what is tired, check the dispersion, and leave the group sealing the way it should. Doing it then is cheaper than finding out mid-service, with a queue, that the portafilter will not lock.

If the group is already leaking, or the portafilter spins without catching, book it rather than forcing the handle. A hardened gasket can score the group face if it is left, and that is a much bigger job than a seal.

Common questions

How often should a group head gasket be replaced?

On a busy commercial group, every 3 to 6 months, or sooner if the portafilter no longer locks squarely or coffee leaks around the ears. It is a small part, and a very common reason a group starts weeping.

How often should a shower screen be replaced?

Inspect it whenever extraction goes uneven, and at every service. Replace it when the holes are blocked, the screen is bent, or coffee oils will not clean off. It is often changed at the same time as the gasket.

Can I change a group gasket myself?

Sometimes, if the group is cool and the machine is isolated. The new gasket has to seat properly or it will leak again. Most sites have it done during front-end servicing, so the screen and the dispersion are checked at the same time.