Your boiler has sensed that the exhaust fumes are getting too hot and has shut down as a safety precaution to prevent damage.

fault flue gases probe / flue gases overtemperature probe

What causes this fault?

This fault occurs when the internal temperature of the exhaust gases exceeds safe limits, potentially causing damage to the boiler's internal plastics. The most common reasons are a build-up of debris or limescale inside the heat exchanger, which prevents heat from transferring to the water, or a failure of the internal insulation panels meant to contain the burner's heat.