Your boiler is currently warming itself up and checking that water is flowing correctly before it starts heating your home.

Status indicator during start-up/heat demand sequence

What causes this fault?

This code appears when the boiler is running a brief pre-check to ensure there is sufficient water pressure and flow before the main burner ignites. It is caused by the internal pump building up pressure to confirm the system is safe to operate. If this code stays on the screen for a long time, it could indicate that air is trapped in the system or the pump is struggling to move water effectively.