BoilerFaultCodesYour boiler is detecting a flame remaining inside the unit for a few seconds after it should have been shut off.
Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now — this fault can be dangerous if ignored.
Technical description: The flame is extinguished too late after the gas valve closes
What causes this fault?
This fault occurs when the boiler's sensors detect a flame for several seconds after the heating cycle has finished and the gas should have stopped flowing. The most common reason is a gas valve that is physically sticking open or an electrical fault in the control board that fails to cut power to the valve. In some cases, a carbon-coated sensing electrode may also be providing a false signal back to the boiler.
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 A20 — 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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