BoilerFaultCodesYour boiler has stopped working because it cannot confirm that harmful exhaust gases are being safely cleared through the flue pipe.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Lockout Burner Mains - Manual Air Proving LOCKOUT (APS is not maintaining its signal. This has occurred 4 times)
What causes this fault?
This fault occurs when the boiler's internal safety sensor cannot detect a steady flow of air through the system, meaning it isn't sure that exhaust fumes are leaving the house safely. The most common reasons are a failing fan that isn't spinning fast enough, a blockage in the flue pipe, or a perished rubber tube that has stopped the sensor from reading air pressure correctly.
This fault is more common during periods of high winds, which can create back-pressure in the flue and interfere with the air pressure sensor's readings.
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 Air Proving LOCKOUT — no call-out fees, no surprises.
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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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