BoilerFaultCodesWhat the manual says
Manufacturer manualManual Lockout. The APS (Air Pressure Switch) is not maintaining its signal. Has occurred 4 times while burner lit.
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 is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Avoid the next call-out bill
A cover plan would handle faults like Air Proving LOCKOUT: no call-out fees, no surprise bills.
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