BoilerFaultCodesTechnical description
Air transport: Air differential switch does not open: Air differential switch defective; Extreme draft through flue gas discharge duct; Short-circuit in wiring.
What causes this fault?
This fault occurs when the boiler's internal safety sensor incorrectly detects that air is moving through the system before the fan has even started. The most common reasons are a sensor that has physically jammed in the 'on' position or debris and moisture blocking the small silicone tubes that monitor air pressure. It can also be caused by heavy winds blowing directly into the external flue pipe, forcing the sensor to trigger prematurely.
This issue often occurs during periods of extreme wind or stormy weather, as gusts can create enough pressure in the flue to confuse the air pressure sensor.
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.