BoilerFaultCodesTechnical description
Burner in fault state - Flue gas/air supply system blocked
What causes this fault?
This fault occurs when the boiler's safety sensors detect that the exhaust gases cannot escape or fresh air cannot be drawn in correctly. The most common reasons are a physical obstruction in the flue pipe outside, a failing internal fan, or a faulty pressure switch that incorrectly thinks the pathway is blocked. Because the boiler cannot guarantee a safe flow of air for combustion, it shuts down immediately to prevent harmful gases from entering the home.
In winter, this code can be triggered by heavy snowfall blocking the external flue terminal or by birds seeking warmth and building nests in the pipework.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.