Your boiler has detected an electrical fault with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.

Burner blocked: Flue gas temperature sensor short circuit

What causes this fault?

This fault occurs when the boiler's internal computer detects a physical failure in the sensor that monitors the heat of the exhaust gases. The most common reason is that the sensor's internal wiring has degraded or failed entirely, leading to an incorrect electrical signal that forces the boiler to shut down to prevent overheating.