Your boiler has detected a problem with its primary temperature sensor and has shut down as a safety precaution to prevent overheating.

Sensor fault S1

What causes this fault?

This fault occurs when the boiler's main flow sensor sends an incorrect or interrupted signal to the control board, suggesting the sensor has either failed or become disconnected. The most common reason is general wear and tear of the internal thermistor or moisture damage affecting the electrical contacts within the sensor wiring.