Your boiler has detected a problem with the sensor that monitors hot water temperature, likely due to a loose connection or a fault in the internal wiring.

Check that the DHW thermistor wires are unconnected and are not faulty or trapped.

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor responsible for monitoring your hot water temperature. The most common reason is a loose electrical connection or a break in the internal wiring, preventing the system from knowing if the water is at a safe temperature. Because the boiler cannot verify the heat level, it stops providing hot water as a safety precaution.