FJV is self-acting temperature controller used to control: return water temperature from hot water tanks in direct connected district heating systems and return water temperature in district heating systems with mixing loop. The FJV ensures that return water is cooled to required temperature before it flows back to the district heating plant. Controller closes on rising temperature. The controller has a control valve, thermostatic actuator and handle for temperature setting. Thermostatic actuator consist of a bellows only. For block and district heating systems.