Your boiler has detected that the sensor monitoring the temperature of the exhaust fumes is sending an incorrect signal or has failed.

Exhaust gas temperature sensor error – electronic card detecting an anomaly in the gas exhaust gas sensor.

What causes this fault?

This fault occurs when the boiler's internal computer receives an implausible or missing signal from the sensor that monitors the heat of the exhaust gases. The most common reason is that the sensor itself has developed a fault or been damaged by excessive heat, though it can also be caused by loose wiring or a communication error within the main control board.