!!
critical HP
Error Code Printhead Alert light flashing and both Printhead icons blinking
Both printheads are missing, installed incorrectly or incompatible/damaged.
? What Causes This
Incompatible printheads or incorrect installation of both printheads.
✓ How to Fix It
Ensure that correct HP printheads are used based off printer specifications and install properly. Contact service if issue persists.
Source: page 50 of the official manual
From the manual
This error code appears in:
HP Ink Tank 310