BoilerFaultCodesTechnical description
Air transport: a. Fouling/clogging of the air supply, flue gas discharge or heat exchanger; b. Differential air pressure switch does not function: differential air pressure switch defective; gas/air connections loose or clogged; gas/air connections mixed up; spring loaded damper does not open.
What causes this fault?
This fault occurs when the boiler cannot move air through the system safely due to a physical blockage or a sensor failure. The most common reason is a buildup of debris in the heat exchanger or a problem with the fan that prevents the unit from clearing out exhaust gases. It can also be triggered if the pressure switch, which monitors this airflow, becomes faulty or has its small sensing tubes blocked.
This fault is occasionally more frequent in autumn or early winter, as debris or bird nests in the flue terminal can restrict airflow when the boiler starts working harder.
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.