Your boiler has detected a fault with the sensor that monitors the temperature of the water leaving the unit, preventing it from heating your home safely.

Central heating (CH) water flow negative thermistor coefficient (NTC) sensor defective check CH flow NTC sensor and connection leads.

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the sensor that measures the heat of the water heading to your radiators. The most common reason is that the sensor has physically failed or developed a short circuit, though it can also be caused by loose or damaged wiring connecting the sensor to the main control board.