Abstract: A vertical float switch, suitable for use as a low water cut-off control or the like, having differential adjustment means is disclosed. The float switch includes a hollow housing forming a float chamber which communicates with a hot water boiler vessel by way of vertically spaced equalizing lines. A non-magnetic sealing tube extends vertically away from the housing and communicates with the float chamber of the housing. A float rod is slidably mounted within the housing by way of a generally cylindrical guiding collar. A float is mounted to the lower end of the rod for translating the rod in accordance with the level of the water within the float chamber. An armature of magnetic material is fixedly mounted to the other end of the rod for translation with the tube in accordance with the level of the water within the boiler. A switch frame is clamped at a predetermined point along the tube, and includes a bracket pivotally mounted thereon for translation toward and away from the tube.