Your boiler has detected an issue with the system that removes waste water or measured a temperature imbalance, causing it to shut down as a safety precaution.

Condensate pump / flue gas thermistor fault

What causes this fault?

This fault occurs when the boiler detects a failure in the pump responsible for removing waste water (condensate) or a safety sensor indicates the internal temperatures are incorrect. The most common reason is a blocked or failed condensate pump, which prevents the boiler from safely draining liquid produced during operation. If the water cannot escape, or if a sensor detects abnormal heat levels, the system shuts down to prevent internal damage or flooding.