The HOT AIR FAULT light illuminates amber, accompanied by an associated ECAM caution, when duct overheat is detected. The fault circuit activates when the duct temperature reaches 88°C. In this case, both the valve and the trim air valves automatically close.

The FAULT light goes off when the temperature drops below 70°C, or when the flight crew selects the OFF position.

The valve will close automatically if:

• The duct overheats,
• The cockpit trim air valve fails, or
• Both cabin trim air valves fail.

However, the hot-air pressure-regulating valve remains operative even if either the forward or aft cabin trim air valve fails.