A Cylinder Thermostat monitors the temperature of the domestic hot water. A Cylinder Thermostat switches the heat supply from the boiler to the hot-water cylinder on and off. It works by sensing the temperature of the water inside the cylinder, switching on the water heating when the temperature falls below the thermostat setting, and switching it off once the setting has been reached. The Cylinder Thermostat is strapped onto the hot water cylinder between one quarter and one third of the way up. Cylinder Thermostats should be set to about 55-60°C.