Your boiler has detected that there is too much water pressure in the system, which can cause the safety valve to leak.

DIY fix possible

Locate the bleed valve on a radiator (usually a small square pin).Use a radiator key and a cloth to slowly open the valve and release a small amount of water into a container.Check the boiler pressure gauge frequently to ensure it returns to the normal green zone, typically between 1 and 1.5 bar.