Rocket O-ring for the rotary knob – so steam and water feel solid again
The rotary knob is the control you touch most often. If it suddenly turns too easily, wobbles or gets damp at the spindle, it is almost always down to this O-ring. It sits on the shaft of the steam and water tap, keeps it guided and seals it to the outside.
Heat, limescale and a few thousand turns make it hard. The knob then develops play and the machine looks damp in a spot that should be dry. Part number C400002786.
When it is due
When the rotary knob develops play or turns noticeably too easily. When moisture escapes at the shaft. And routinely whenever you take the tap apart anyway – a spare O-ring is cheaper than a second job.
At a glance
| Type |
O-ring, wear part |
| Installation location |
Steam and water rotary knob, on the shaft |
| Fits |
Rocket Cellini and Giotto |
| Scope of delivery |
one O-ring |
| Part number |
C400002786 |
| Version |
Original Rocket spare part. We have no documentation of the inner diameter, cross-section thickness or material for this number. |
| Brand |
Rocket Espresso |
Who it is for
For anyone with a Cellini or Giotto whose knob no longer feels solid. And for anyone who renews all the sealing points on the tap in one go during the annual overhaul.
O-rings and sealing rings in the Rocket catalogue
Rocket fits a whole series of O-rings in the steam path, water path and boiler that look very similar from the outside. For most of them, the documentation states neither the inner diameter nor the cross-section thickness – they can only be told apart reliably by part number. That is why we list them individually, with the number in the title or in the table:
-
O-ring steam and water tap – A449904334
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O-ring for the steam and water tap cover – A449904672
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O-ring steam and water rotary knob, Cellini and Giotto – C400002786
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O-ring water nozzle, Appartamento to Mozzafiato – C400003008
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O-ring 3-way valve – M449907403
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O-ring S2 valve – M449907143
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O-ring 4250 silicone, R9 – M449905837
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O-ring 3187 Viton, R9 – R499907384
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O-ring drain elbow, Boxer, RE A and R9 – M449905463
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Copper sealing ring heat exchanger – C479900673
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O-ring boiler top, Porta Via – A449906261
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O-ring boiler bottom, Porta Via – A449906262
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O-ring heating element, Porta Via – A449910266
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O-ring 18 × 5 mm machine foot, R Cinquantotto – A449906954
If you measure your removed part and don't know the number, send us the model and serial number – we will check it against the exploded view.
What goes with it
There is a separate ring at the outlet: the Rocket O-ring for the water nozzle. To stop limescale getting there in the first place, the cleaning range for machine and grinder helps, together with the descaling pad for the water tank. Everything else under Rocket accessories and spare parts.
Tip from our café
We always fit O-rings with a touch of food-grade silicone grease – it then slides into its groove instead of twisting during assembly. A twisted O-ring seals at first and tears after a few weeks. This is our workshop routine from Bern and Zurich, not a manufacturer specification. For dialling in afterwards we use Nutty Delight, Cozy Chocolate for chocolatey notes and Very Nutty for maximum body. All roasts under Coffee beans.
Returns excluded
Service parts are excluded from exchange and return. They are sourced specifically for each order and cannot be resold after installation or a test fit 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 case of defective goods remain unaffected.
Frequently asked questions
How many O-rings do I need?
One per rotary knob. If you operate steam and hot water separately, you need two.
Is this the same ring as on the water nozzle?
No. The ring on the nozzle is a separate part with the number C400003008 – both are available individually from us. If in doubt, send us a photo of the spot.
Do I need tools?
To take the tap apart, yes. Never work on the ring itself with sharp tools, otherwise the new one is damaged straight away.
Does it fit an R58 or Appartamento?
This part is listed for the Cellini and Giotto. For other Rocket models we stock other seals – write and tell us which model you run.
Can I see the part in the showroom?
Our showrooms in Bern (Gerberngasse 44) and Zurich (Hagenholzstrasse 50b) show a wide selection, but not our entire range – the display changes. Drop us a quick line at [email protected] before your visit, and we will check whether the product you have in mind is currently there.
Questions? Write to [email protected]. Delivery across Switzerland and to Liechtenstein in 2-4 working days.
