A liquid-filled dual control thermostat which adopts two levels of protection. The dual thermostat includes both a temperature control and a high limit safety cut-out and manual re-set. This thermostat is designed to be fitted to the hot water cylinder and in the event of a failure the thermostat will either cut off due to the control thermostat reaching its set temperature which is user adjustable or by the high limit cut-off thermostat which is set to a pre-determined temperature.