The fluid sampler WaSam is being developed for downhole sampling in deep geothermal boreholes. A new sampling and storage concept is developed and realized in a functional demonstrator (sampling volume 480 cm³). Via the wireline, the demonstrator sampling system is remote controlled with real time data. Temperature, pressure in different locations of the probe, and electronic components are permanently monitored and recorded. The in-situ storage of the monophasic sample is being realized by an adaptive hydraulic and heating control. Furthermore, the functional demonstrator fulfills the requirements of the design standard for downhole logging tools (T= 200°C, p= 60 MPa, harsh and corrosive fluids). A high loadable demonstrator housing made of Inconel® 718 was reused from standard parts of the design construction kit.