A surface treating head assembly for an appliance such as a vacuum cleaner includes a head and a drivable agitator in the form of a brush bar, rotatably housed in a housing. A motor is arranged to drive a mechanism, such as cams arranged to adjust the position of the brush bar with respect to the housing. An electro-mechanical feedback arrangement, which may include an actuator, is arranged to bear against microswitches to control operation of the motor. Different faces of the actuator are arranged to act against different ones of the microswitches in accordance with different positions of the brush bar. The height of the brush bar is selectively controllable between the predetermined positions, such that the depth of penetration of the bristles of the brush bar may be optimized for different types of carpet.