Your boiler's temperature sensor responsible for monitoring stored hot water has developed a fault, preventing it from reading the temperature correctly.

Heat store NTC sensor 2 defective

What causes this fault?

This fault occurs when the electrical resistance in the sensor used to monitor your hot water storage reaches an impossible value, suggesting the component has failed internally. It is usually caused by natural wear and tear of the sensor's delicate internal elements or, occasionally, a loose connection in the wiring harness that links the sensor to the main control board.