Your boiler has detected that a safety sensor in the exhaust pipe is reporting an incorrect temperature reading or has developed a fault.

What causes this fault?

This fault occurs when the sensor responsible for monitoring the temperature of the exhaust gases sends an illogical reading to the boiler's internal computer. It often happens because the sensor has physically degraded, developed a loose wiring connection, or the boiler is running too hot due to an internal blockage or heat exchanger issue. To ensure safety, the boiler shuts down to prevent any risk of the plastic flue components melting or overheating.