Your boiler is checking whether there is enough water pressure to run safely, but it hasn't yet reached the point of locking out with a permanent error.

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 to top it up to 1.5 bar.Ensure all radiator valves are fully open to allow water to flow freely.