BoilerFaultCodesYour boiler has detected that a safety flap in the flue pipe is stuck closed, preventing exhaust gases from escaping.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Fluenon-returnflapclosed
What causes this fault?
This fault occurs when a mechanical flap inside the exhaust system fails to open, which safely prevents outdoor air or fumes from flowing back into the boiler. The most common cause is the flap becoming physically stuck due to a build-up of debris or the fan failing to generate enough pressure to push it open.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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