replaced all four ink cartridges but the black is not working

[Gimp2]

HP Office Jet Pro 8028

Model # 3UC64A

[Elohi_NR]

Hi @Gimp2,

Welcome to the HP Support Community. 

I'd be happy to help you! 

I understand that you are facing issues with printing in black

Try updating firmware by selecting the current OS. Click here

Perform the following tasks in the order given. Use the printer after each task to see if the issue is resolved.

Clean the printhead

• The printhead could be clogged, and you might need to clean the printhead several times to restore print quality. Use an automated tool from the printer control panel to clean the printhead.
• CAUTION: Never turn off the printer without ink cartridges installed. To avoid issues that require cleaning the printhead or that can damage the ink system, always replace ink cartridges as soon as possible, and always turn off the printer using the Power button.
• On the printer control panel, open the Setup menu, and then touch Printer Maintenance or Tools.
• Touch Clean Printhead, and then touch Continue.
• After the cleaning completes, a Test Page prints.

• Examine the Test Page.
• If the print quality is unacceptable, touch Clean Again to continue the next level of cleaning. If necessary, repeat these steps for the third cleaning cycle.
• NOTE: If the printhead is badly clogged, it might require another cleaning cycle. If so, wait 30 minutes before you perform all three levels of cleaning again.
• If the print quality is acceptable, touch Done.

Click here for the remaining steps. 

Hope this helps! Keep me posted for further assistance.
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