Your boiler is confused by how long it is taking to heat your hot water and is stuck in a constant cycle.

Constant hot water cycle time

What causes this fault?

This fault occurs when the boiler detects that it is taking far too long to reach the required temperature for your hot water, causing it to get stuck in a repetitive heating loop. It is usually caused by a faulty sensor sending incorrect temperature readings to the brain of the boiler or a mechanical part failing to direct heat to the water properly. In some cases, the main control board may simply be misinterpreting the data it receives from the system.