No, you cannot boil a thermostat to see if it works. Doing so could damage the thermostat and render it unusable. Thermostats contain a liquid that expands and contracts as the temperature changes. When the liquid reaches a certain temperature, it activates a switch that turns the heating or cooling system on or off. If you were to boil the thermostat, the liquid would expand too much and break the glass enclosure. It's also possible that boiling the thermostat could cause the internal components to malfunction.