Embodiments are directed to a temperature calibration system that includes a closed fluidic system, such as a thermosiphon or a heat pipe. The closed fluidic system includes a valve for fluidly separating components therein from each other. In one embodiment, the closed fluidic system is a thermosiphon (or a heat pipe) and the valve is configured, in a closed state, to cover a port of the condenser to fluidly separate the condenser from other components of the thermosiphon. The valve may be a passively activated valve or an electrically actuated valve. In some embodiments, the valve is thermally actuated such that the valve changes state in response to changes in temperature.