Your boiler has stopped providing hot water because the internal sensor responsible for measuring water temperature has either failed or has a loose connection.

Domestic hot water thermistor/wiring fault

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor that monitors hot water temperature. The most common reason is that the sensor has internal electrical failure due to constant heat cycling, or the wiring connecting it to the main board has come loose or become corroded.