Your boiler has detected that the water pressure inside the heating system has risen too high, which may cause it to stop working to protect the internal components.

DIY fix possible

Locate a radiator in your home, preferably one upstairs.Place a cloth or small container under the radiator bleed valve.Open the bleed valve slightly using a radiator key until water starts to trickle out.Allow a small amount of water to drain until the pressure gauge on your boiler drops to the green zone (typically 1.0 to 1.5 bar).Close the valve tightly and check that the boiler restarts.