BoilerFaultCodesYour boiler is failing to light the flame needed to heat your water and radiators, which has caused the system to shut down for safety.
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. No flame signal is present. Cause: Check the ionisation electrode and leads, measure the ionisation current, check the gas pressure, check the gas combination valve, ignition, ignition module, ignition electrodes and the condensate drain. Press E.
What causes this fault?
This fault occurs when the boiler's internal computer tries to start the burner but cannot detect a flame after several attempts. The most common reasons are a dirty or worn-out sensor that can no longer 'see' the flame, or a physical blockage in the gas supply or drainage system preventing ignition. Because the boiler cannot confirm it is burning fuel safely, it shuts down completely to prevent gas from building up.
This fault is more common during freezing winter temperatures, as a blocked or frozen condensate drainage pipe can back up and prevent the boiler from lighting.
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 F4 — no call-out fees, no surprises.
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