Your boiler has detected a minor electronic sensor issue and is running at a lower power level to keep your home warm until it can be serviced.

The boiler will continue to operate with a reduced performance in some fault conditions.

What causes this fault?

This fault occurs when one of the internal temperature sensors sends an inconsistent signal to the main control board, suggesting the sensor is starting to fail or has a poor electrical connection. Instead of shutting down completely, the boiler enters a safety mode to prevent overheating while still providing basic heating. The root cause is typically wear and tear on the thermistor component or moisture affecting the wiring harness.