Welcome to the HP Support Community.
Have you tried all the steps from this document: https://support.hp.com/in-en/product/hp-officejet-pro-6830-e-all-in-one-printer-series/5390307/document/c03026717
If yes, I recommend you contact the HP Phone Support Team as this could be a hardware/printhead issue.
You can get the phone number for the team from the below link:
* Click on this link – www.hp.com/contacthp/
Let me know if this helps.
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Have a great day!