Your boiler has lost connection with its internal hot water storage sensor and cannot currently heat your water effectively or safely.

Control mode - Sensor S3 lead break

What causes this fault?

This fault occurs when the boiler's control board can no longer communicate with the sensor responsible for monitoring the temperature of your hot water. The most common cause is a physical failure of the internal sensor probe or a loose connection in the wiring harness that links the sensor to the main computer. Without this signal, the boiler cannot safely determine how hot the water is, so it stops heating the cylinder to prevent overheating.