Hi pzig,
Welcome to the HP Forums, I hope you enjoy your experience!
I understand the black isn't printing.
I will be happy to help you.
Here is a document for Troubleshooting Print-Quality Issues to see if we can resolve this issue.
This document provides the steps for manually cleaning the printhead.
Are you using Genuine HP Cartridges?
What are the ink levels showing?
What were the results of the Print Quality Diagnostic Report?
Thank you for posting on the HP Forums.
Have a nice day!