BoilerFaultCodesYour boiler has detected dangerous exhaust fumes leaking back into the unit, which is a serious safety risk and has caused the system to shut down.
Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now — this fault can be dangerous if ignored.
Technical description: Flue gas detected inside boiler. Flashing light occurs for 20 minutes unless power is interrupted. May be caused by flue blockages or heat exchanger restrictions.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that poisonous exhaust gases are leaking back into the casing instead of being safely expelled outside. The most common reasons are a blockage in the flue pipe, a cracked internal seal, or heavy debris buildup within the heat exchanger that prevents the fumes from flowing away correctly.
This fault can be more frequent in autumn or winter if debris like fallen leaves or nesting birds have blocked the external flue terminal.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like Flue Spillage Fault — no call-out fees, no surprises.
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