Your boiler is struggling to detect that it has enough water inside to operate, often because the filling valve has been left open or the internal pressure is dropping.

DIY fix possible

Check that the external filling loop or internal filling valve is fully closed.Check your boiler's pressure gauge and ensure it is between 1.0 and 1.5 bar.If the pressure is low, use the filling loop to top it up to 1.5 bar, then ensure the valve is tightly shut.