Abstract: A predetermined limit in the rotation of a manually rotatable control shaft is established by a special knob having a speed nut which secures the knob to the shaft, and an interrupted circular slot in the knob, concentric with the shaft, for cooperating with a fixed projection extending parallel to the shaft and into the circular slot. The device is described as usable in a thermostatically controlled heating system with an auxiliary control for improving efficiency.

Abstract: Efficiency of domestic heating systems is improved by a flue temperature responsive switch for intermittently shutting down the burner when temperature conditions are such as would cause extended operation of the burner in the absence of the switch. The temperature at which shut-down occurs is adjustable, and the temperature at which burner operation is reestablished is dependent on the shut-down temperature. However, the minimum temperature at which burner operation is reestablished by the switch is fixed at the time of installation of the switch by securing a control knob having a stop at a selected position on a control shaft which adjusts the shut-down temperature. The switch contacts are constructed so that the switch closes if any of its principal movable parts fail.