Your boiler is unable to provide hot water because it cannot accurately measure how hot the water is.

Hot water temperature sensor is defective – the plug to the hot water temperature sensor may not be connected

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor that monitors your tap water temperature. The most common reason is that the sensor itself has developed an internal electrical failure or the wiring connecting it to the main system has come loose or become corroded. Because the boiler cannot safely verify how hot the water is, it stops heating it entirely to prevent the risk of scalding.