Your boiler has detected an issue with the sensor that monitors exhaust gases, causing the system to lock down for safety.

Flue probe fault

What causes this fault?

This fault occurs when the sensor responsible for measuring the temperature of the exhaust gases sends an incorrect or missing signal to the boiler's control board. The most common reason is that the probe itself has failed due to constant exposure to high temperatures, or the electrical wiring connecting the sensor has become loose or damaged.