Thermal controls

A thermal control (1) for a liquid heating appliance includes a tristable subassembly (20) that can be added to the thermal control (1) to provide selection of boil and sub-boil modes. The subassembly (20) relies on the bias of a trip lever spring (3) in the thermal control to achieve a stable off position, without requiring any additional spring in the subassembly. The subassembly includes a mode selection lever (21) that is moveable by a user actuator, such that the subassembly can be manually moved from the boil or sub-boil modes to an off position. The user actuator may have a pivot point displaced beyond the pivot point of the mode selection lever (21), to reduce the travel of the end of the user actuator. A lift-off switch-off mechanism may be provided by means of a bifurcated spring.