Air treatment apparatus

An air treatment apparatus comprising:

• a primary airflow passage extending from an inlet to an outlet;
• a primary air mover disposed in the primary airflow passage to move air along the primary airflow passage from the inlet to the outlet;
• an air treatment device arranged to treat air flowing along the primary airflow passage;
• a secondary airflow passage extending between:
• a first opening arranged to receive air that is untreated by the air treatment device;
• and
• a second opening connected to the primary airflow passage downstream of the air treatment device;
• and
• one or more sensors arranged to sense a characteristic of the air flowing along the secondary airflow passage;
• an airflow director for directing airflow;
• and
• a controller configured to control the airflow director between:
• a baseline configuration in which air flows from the first opening to the one or more sensors;
• and
• a diagnostic configuration in which air flows from the second opening to the one or more sensors.