Your boiler has detected a problem with the sensor that monitors exhaust gases, and it has shut down as a safety precaution.

Flue sensor damaged

What causes this fault?

This fault occurs when the internal sensor responsible for monitoring the temperature of the exhaust gases becomes faulty or loses its connection to the control board. The boiler shuts down as a safety measure to prevent the appliance from overheating or operating with unsafe flue gas temperatures. The primary cause is typically a degraded NTC sensor or heat damage to the wiring harness connected to it.