This work accompanies the cold test phase of a thermal energy storage prototype of the Vienna University of Technology. The main component is a sensitive heat exchanger, which carries sand as Hot Storage Media and thus bears the name SandTES. In order to ensure a safe and reliable operation of this 200 kWth system also for the high temperature range, various tests are carried out in a cold test phase. In this thesis, all experiments carried out are described and analyzed. Also realized work on the plant as well as preparations for the hot phase are given.