A surface treating head includes a main body, a suction cavity in the main body including first and second suction channels, each of which is bounded on one side by a working edge, an air duct interposed between the first and second suction channels for conveying air towards the working edges, a brush unit and a drive mechanism for moving the brush unit between a stowed position in which the air duct is open to the atmosphere and a deployed position in which the air duct is closed.