Your boiler has detected that the water pressure is too low or fluctuating, causing it to pause for safety until it returns to a normal level.

DIY fix possible

Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.If the pressure is below 1 bar, locate the filling loop (usually a silver flexible hose) under the boiler.Slowly open the valves on the filling loop to add water until the gauge reaches 1.2 bar, then close the valves tightly.