Your boiler is struggling to move water around the system correctly, which is causing it to shut down to prevent overheating.

Primary circulation fault or pump failure

What causes this fault?

This fault occurs when the water inside the boiler gets too hot too quickly because it isn't being pushed away into your radiators or hot water tank. The most common reason is that the internal pump has failed or is physically jammed, but it can also be caused by a build-up of sludge blocking the pipework or an airlock trapped in the system.