A surface treating appliance includes a surface treating head, a hose, and a main body including a fan unit for generating a flow of fluid, and a rotary changeover valve including a valve member which is selectively rotatable between a first position allowing fluid flow between the hose and the fan unit, and a second position allowing fluid flow between the surface treating head and the fan unit, the valve member comprising a hub having an internal surface shaped to receive a boss about which the valve member is selectively rotatable. To facilitate the breaking of seals by valve member and other parts of the appliance as the valve member moves away from one of its first and second positions, the external surface of the boss and the internal surface of the hub each has a profile generally in the form of a triangular prism, the profile of the external surface of the boss tapering towards the valve member. As a result, the valve member is forced to move along the longitudinal axis of the boss as it is rotated thereabout.