BoilerFaultCodesYour boiler's small starter flame is struggling to stay lit because of a buildup of dust or debris, preventing the main heating from firing up.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Partially blocked pilot filter or pilot injector.
What causes this fault?
This fault occurs when the small pilot flame becomes too weak or unstable to heat the safety sensor. The most common cause is a buildup of microscopic dust or carbon soot that partially chokes the tiny hole in the pilot burner, preventing the boiler from safely transitioning to the main heating stage.
This issue often surfaces in autumn when a boiler is turned on for the first time after being dormant all summer, as settled dust is more likely to cause a blockage.
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 B(4) — no call-out fees, no surprises.
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