BoilerFaultCodesTechnical description
Flue gas sensor error for having exceeded the max. flue gas temperature (with this error the fan operates at maximum speed )
What causes this fault?
This fault occurs when the internal sensors detect that the exhaust gases leaving the boiler are far too hot, which can damage the internal components or the flue system. The most common reason is a buildup of limescale or debris inside the main heat exchanger, which prevents the heat from being transferred to your water and instead sends it straight out through the exhaust. It can also be triggered if the flue gas sensor itself has failed and is sending an incorrect reading to the boiler's computer.
This fault is more common in winter when the boiler is running at maximum capacity for long periods to heat a cold home, putting the most stress on the heat exchanger.
Engineer required
This is a emergency severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.