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.

Flue sensor short circuit – check connections to flue sensor are in place

What causes this fault?

This fault occurs when the boiler's internal computer detects an electrical failure or a 'short circuit' in the sensor that monitors exhaust temperatures. The most common reason is that the sensor has failed internally due to heat exposure, or the wiring connecting it to the main control board has become damaged or loose.