BoilerFaultCodesYour boiler is receiving a request to turn on the heating or hot water, but it has not yet successfully fired the burner.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: DEMAND ON
What causes this fault?
This fault occurs when the boiler recognizes you want heating or hot water but fails to complete its internal safety checks to ignite the flame. It is usually caused by a mechanical failure in the fan or the air pressure switch, which prevents the boiler from proving it can safely expel exhaust gases. As a result, the system stays in a 'holding' pattern and refuses to fire the burner for safety reasons.
This issue often surfaces during the first cold spell of autumn when a fan that has sat idle all summer struggles to spin up to the required speed.
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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