Abstract: A plate heat exchanger comprises a plate package (1) with heat exchanger plates (2) forming primary plate interspaces (3) for a primary medium and secondary plate interspaces (4) for a secondary medium. A primary inlet (11) transports the primary medium to the primary plate interspaces. A primary outlet (12) transports the primary medium from the primary plate interspaces. A secondary inlet (21) transports the secondary medium to the secondary plate interspaces. A secondary outlet (22) transports the secondary medium from the secondary plate interspaces. A sensor device (30) comprises a space (31) containing a sensor medium influenced by the temperature of the secondary medium. A throttle member (35) connected to the sensor device controls the flow of the primary medium in response to the sensor medium.