Your boiler has detected that the water pressure inside your heating system is too low and needs to be topped up to function correctly.

DIY fix possible

Locate the external filling loop (a flexible metal or silver hose connected between two pipes under your boiler).Open the valves on both ends of the hose slowly to allow water into the system.Watch the pressure gauge on the boiler front until the needle reaches the green zone (usually 1.5 bar), then turn both valves securely off.