BoilerFaultCodesYour boiler has detected an issue with the ventilation system, meaning it cannot safely clear waste gases and has shut down as a precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Air flow proving fault - that is fan or air pressure switch.
What causes this fault?
This fault occurs when the boiler's internal safety system can no longer confirm that the fan is successfully pushing harmful exhaust gases out of the flue. The most common reason is that the fan has failed, the air pressure sensor has malfunctioning electrical contacts, or the small tubes connecting them have become blocked with dust or debris.
This fault is more common during the first cold spells of autumn, as mechanical fans that have been idle over the summer can seize up when they are suddenly required to run frequently.
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.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like Neon3 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Glow-worm Fuelsaver Complheat 40 55 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.
Affiliate links — we may earn a commission at no extra cost to you.