This wil verry much speed up the process.
Du to you're tip I now found a zip file of 16GB in the /tmp folder.
The /home folder was also 18GB, so that would explain the "no disk space".
I do however think the zip file should not be there anymore.
Maybe something left behind?
Or should I be aware of double disk usage with ispconfig?
Anyway after I deleted this and clean up the home folder I wil do an installation again.
Hope this wil bring everyting back online.