BoilerFaultCodesYour boiler has shut down because it thinks it can see a flame before it has even started the ignition process.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Burner in fault state. The flame signal is already present at burner start. Cause: Check the ionisation electrode and leads. Press E.
What causes this fault?
This fault occurs when the boiler's internal computer detects a flame signal at a time when there shouldn't be one, such as during the initial safety check before ignition. The most common cause is a faulty or soot-covered ionisation electrode that is sending a false electrical signal, or moisture trapped within the burner's wiring. Because the boiler cannot verify that the burner is truly off, it shuts down as a safety precaution to prevent a buildup of unburnt gas.
This fault can be more frequent during periods of high humidity or heavy rain, as moisture entering the air intake can interfere with the sensitivity of the ionisation probes.
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 F3 — no call-out fees, no surprises.
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