BoilerFaultCodesYour boiler thinks there is still a flame burning even though it has commanded the gas to turn off.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Ionisation signal present even though burner is switched off
What causes this fault?
This fault occurs when the boiler's internal sensor detects a flame signal at a time when the gas should be completely shut off. The most common reason is a sensor that has become covered in carbon deposits or moisture, though it can also be caused by a gas valve that is failing to close fully or a fault within the main control board.
This issue can be more frequent during periods of high humidity or heavy rain, as moisture entering the air intake can interfere with the sensitive electronics of the ionisation probe.
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 F7 — no call-out fees, no surprises.
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