Your boiler has lost water pressure and needs to be topped up to function correctly again.

DIY fix possible

Locate the external filling loop, which is a silver braided hose connecting two pipes near your boiler.Open the valves at both ends of the hose to let water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves tightly and remove the hose if it is not a permanent fixture.