The coffee machine was switched on when the milk valve was removed. The appliance door was closed while removing the milk valve.
Close and open the appliance door.
Insert the holder without the stainless steel bolt and silicone seal until it audibly engages.
If the holder is unable to engage, close the appliance door again and reopen it until the holder is able to engage.
When the holder engages, close the appliance door and wait until initialisation is complete.
The drinks menu is displayed.
Then reinsert the entire milk valve as follows:
Open the appliance door and remove the holder. Leave the appliance door open.
Insert the stainless steel bolt from above.
Insert the silicone seal into the milk valve holder.
Insert the holder and silicone seal until they audibly click into place.