BoilerFaultCodesYour boiler has detected a potential issue with the valve that controls the gas supply, meaning it isn't shutting off correctly for safety.
Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now — this fault can be dangerous if ignored.
Technical description: Burner in fault state. Fuel valve closes too late. Cause: Check gas combination valve. Check both control paths. Press E.
What causes this fault?
This fault occurs when the boiler's internal computer detects that gas is still flowing for a few seconds after the burner was supposed to switch off. The most common reason is a mechanical failure within the gas valve itself, where it becomes 'sticky' and fails to snap shut instantly, or a fault in the electronic control board that manages the safety sequence.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like F8 — no call-out fees, no surprises.
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Viessmann Vitodens 333 is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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