Error Code P

Printheads need priming — system ready for initial setup or manual priming of printheads.

? What Causes This

Printer detected new printheads are installed during setup and the ink valve connects ink tanks to printheads; also occurs when system detects low ink levels or dry printhead conditions after a period of inactivity requiring initialization.

✓ How to Fix It

Ensure all ink tanks are filled above minimum line level.
Press and hold Resume button for three seconds to start priming process if detected automatically on control panel display.

Source: page 37 of the official manual

From the manual

This error code appears in:

HP Deskjet GT 5820 All-in-One Printer