Your boiler is struggling to accurately measure the temperature of your hot water due to a faulty internal sensor.

Domestic hot water NTC fault

What causes this fault?

This fault occurs when the sensor responsible for monitoring your hot water temperature has failed or is sending incorrect electrical signals to the main control board. Over time, these sensors can degrade due to constant heat cycles or internal corrosion, meaning the boiler can no longer safely tell how hot the water is. In some cases, the issue may simply be a loose or damaged wire connecting the sensor to the boiler's internal computer.