BoilerFaultCodesYour boiler has sensed a flame when there shouldn't be one, so it has shut down as a safety precaution to prevent damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Safety switch-off: Flame simulation
What causes this fault?
This fault occurs when the boiler's internal sensors detect a flame after the burner should have already shut off, or before it has even started. The most common cause is a moisture buildup or carbon deposits on the sensing electrode, which creates a false electrical signal that tricks the control board into thinking a fire is present.
This fault can be more frequent during periods of heavy rain or high humidity, as moisture entering the flue can interfere with the sensitivity of the electrical ignition components.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like F.27 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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