Your boiler has detected that the water pressure inside your heating system is too low, so it is waiting for a few minutes before trying to start again to prevent damage.

Delay mode due to lack of water in system (~2,5 mins.)

What causes this fault?

This fault occurs when the boiler's control system senses that the water temperature is rising far too quickly, usually because the heated water cannot leave the heat exchanger fast enough. The most common reasons are a failing central heating pump that isn't circulating the water or a physical blockage caused by a build-up of sludge and debris in the pipework.