BoilerFaultCodesYour boiler is failing to start because its internal safety checks haven't confirmed that the fan is pushing waste gases out of the flue correctly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Lighting Sequence-Fan/APS / Check connection & operation
What causes this fault?
This fault occurs when the boiler's safety system detects that the fan isn't moving enough air to safely expel exhaust gases. The most common reasons are a seized fan motor, a faulty air pressure switch that fails to signal the control board, or small tubes becoming blocked with debris or moisture. Without confirming a clear airflow, the boiler will refuse to ignite to prevent a buildup of dangerous fumes.
This issue is more frequent during the first cold spell of autumn, as fan bearings can seize up after sitting idle throughout the summer months.
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 Simultaneous 1 Slow / 1 Fast — no call-out fees, no surprises.
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