Hmmm, thanks for the tip. I read through the "original instructions" again, but there is nothing about descaling.......
The service probably earns nothing else. And yes, you use the machine with a filter, so there shouldn't be much limescale build-up.
But I will look into the matter again. The specialist service can't do witchcraft either :-)

Yes, you can use a standard descaler. I descaled my machine after a year with a Mio-Star (Durgol) liquid descaler from Migros.
descaler from Migros. It says on the label that it is suitable for all coffee machines.