Your boiler is unable to heat your hot water because a sensor responsible for monitoring the cylinder temperature has lost its connection or stopped working.

No DHW heating - Cylinder temperature sensor/comfort sensor/loading sensor lead break

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the sensor that monitors your hot water tank. The most common reason is a physical breakage in the sensor’s wiring or internal electrical failure within the sensor itself, which prevents the boiler from knowing how hot the water is. For safety reasons, the boiler stops heating the water entirely because it can no longer prevent it from overheating.