The gasket that seals every portafilter insertion on the KB90 – with both plates included
Between the portafilter and the brew group sits a rubber ring, and it is the only component that keeps the pressure of the extraction from escaping outwards. On a KB90 it does this several hundred times a day: insert, brew, release, insert. When it gives way, you notice straight away – water comes out at the side, and the portafilter either goes in too easily or no longer sits cleanly at all.
This item comes with two anti-shock plates, as the item name states. We do not know of a part number for this part: it is listed neither in our service parts list nor in the catalogue we otherwise source the numbers from. We won't make one up – send us the serial number of your KB90 and we will match the part.
When it's due
- Water leaks out at the side of the portafilter during extraction.
- The portafilter is hard to insert or, conversely, sits too loosely.
- The gasket has become hard, cracked or dented in one spot.
- After extraction, a rim of wet coffee grounds remains at the top of the filter basket.
- When you release the portafilter, it sprays more than it used to.
At a glance
| Type |
Group head gasket with two anti-shock plates |
| Installation location |
In the group head, between group and portafilter |
| Fits |
La Marzocco KB90. Send us the serial number and we will check the fit. |
| Scope of delivery |
One group head gasket and two anti-shock plates, as the item name states. The diffuser and shower screen are not included. |
| Version |
Original La Marzocco. We have no documentation on dimensions, material and hardness. |
| Installation |
Installation by a specialist recommended |
| Brand |
La Marzocco |
Important notes on installation
The gasket sits in the group head, a component that carries hot water under pressure. Only work on the machine when it is switched off, cooled down and depressurised. After years, an old gasket is stuck tight and has to be levered out; the delicate part here is the sealing surface of the group – a nick in it means even the new gasket will no longer seal.
We deliberately do not provide step-by-step instructions here. If you are unsure, bring the machine to us or have the replacement done as part of a service; there is dedicated tooling for the KB90, which we also stock.
Who it's for
For every KB90 in continuous operation. In a busy café, the group head gasket is one of the parts that are replaced on schedule, not only once something breaks. And for workshops that take care of the replacement as part of a service.
Goes well with
From our workshop in Bern and Zurich
In Bern and Zurich, we don't wait until it sprays to replace the group head gasket; we replace it when the portafilter starts to travel further to the right than usual – that is the earlier sign. And we do it in the morning before opening, not in the evening: the machine is cold, and the first extraction afterwards can be checked calmly. That is our routine, not a manufacturer's specification. We check with the Cozy Chocolate or the Nutty Delight, and for body without acidity with the Very Nutty. All of them are listed under Coffee beans.
No returns
Service parts are excluded from exchange and return. They are procured to order and cannot be resold after being installed or trial-fitted on the machine. So before ordering, check the model, year of manufacture and serial number of your machine – or drop us a line and we will clarify the fit together. Your rights in the event of defective goods remain unaffected.
Frequently asked questions
How do I know the group head gasket is due for replacement?
Water leaking out at the side of the portafilter, a portafilter that is harder to insert, or a handle that travels noticeably further when locking in than it used to.
What are the anti-shock plates?
According to the item name, they are part of the scope of delivery and two are included. We have no documentation on exactly what they do in the assembly, so we do not describe their function here.
Can I do the replacement myself?
We recommend having it done. The sealing surface in the group is delicate, and a scratch in it will make even the new gasket leak.
What is the part number of this part?
We do not know of a number for this item, and we won't make one up. If you have a number from service documentation, send it to us for comparison.
Can I see the part in your showroom?
Yes. Come to our showroom in Bern at Gerberngasse 44 or in Zurich at Hagenholzstrasse 50b, and we will show it to you on the machine.
Questions about the fit? Write to us at [email protected]. We deliver across Switzerland and to Liechtenstein in 2-4 working days.
