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.