Your boiler is performing a temporary check to ensure there is enough water pressure to operate safely.

DIY fix possible

Check the pressure gauge on the front of the boiler or under the casing.If the pressure is below 1.0 bar, use the filling loop handles to top it up to 1.5 bar.Ensure all radiator valves are open and not leaking.Restart the boiler to see if the code clears after the test completes.