BoilerFaultCodesYour boiler is detecting a flame when it shouldn't be there, causing the system to lock out for safety reasons.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The flame signal is already present at burner start.
What causes this fault?
This fault occurs when the boiler's internal sensor detects a flame signal before the ignition sequence has even begun. The most common cause is a faulty ionisation electrode that is sending a 'ghost' signal to the control board, or a gas valve that is leaking fuel into the burner when it should be closed.
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 F3 — no call-out fees, no surprises.
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