BoilerFaultCodesWhat the manual says
Manufacturer manualAir pressure switch (in fan outlet) tube and air/flue gas system. Check hoses are not obstructed and correctly fitted and not damaged. Check air pressure switch or replace. Check flue restrictor corresponds to flue length.
What causes this fault?
This fault occurs when the boiler's safety sensors cannot detect sufficient airflow to safely exhaust burnt gases to the outside. The most common reasons are a failing fan that isn't spinning fast enough, a blockage in the flue pipe, or thin rubber tubes inside the unit becoming perished or blocked with moisture.
This fault is more common during periods of high winds, as strong gusts can create back-pressure in the flue that prevents the air pressure switch from closing correctly.
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 S.33: no call-out fees, no surprise bills.
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