A thermostat valve for two fluids of different temperatures, preferably cold and hot water, having - a valve core assembly unit for insertion as a whole in an opening of a sanitary fitting housing provided for this purpose, which assembly unit comprises -- one intake opening (3a, 3b) for each of the fluids -- an outlet opening for the mixed fluid, -- an adjustment device for adjusting the temperature of the mixed fluid and -- a control element, said element having --- a thermostatic temperature sensor and --- a valve body, ---- which valve body is axially displaceable in the valve core for adjusting the inlet openings (3a, 3b) for the fluids, ---- acts against the force of a return spring and ---- is arranged between valve seats (8, 9) which are provided on the valve core, wherein the valve core assembly unit is provided in two parts such that a first valve seat is formed on a first valve core part, the head piece, and a second valve seat is formed on a second valve core part, the bottom part, wherein the two valve core parts (1, 2) are linearly displaceable relative to each other in such a way that the distance between the valve seats (8, 9) is freely adjustable via a thread by which the first and the second valve core parts (1, 2) are interconnected, and wherein a defined releasable connection is provided between the first and the second valve core parts (1, 2). - a valve core assembly unit for insertion as a whole in an opening of a sanitary fitting housing provided for this purpose, which assembly unit comprises -- one intake opening (3a, 3b) for each of the fluids -- an outlet opening for the mixed fluid, -- an adjustment device for adjusting the temperature of the mixed fluid and -- a control element, said element having --- a thermostatic temperature sensor and --- a valve body, ---- which valve body is axially displaceable in the valve core for adjusting the inlet openings (3a, 3b) for the fluids, ---- acts against the force of a return spring and ---- is arranged between valve seats (8, 9) which are provided on the valve core, wherein the valve core assembly unit is provided in two parts such that a first valve seat is formed on a first valve core part, the head piece, and a second valve seat is formed on a second valve core part, the bottom part, wherein the two valve core parts (1, 2) are linearly displaceable relative to each other in such a way that the distance between the valve seats (8, 9) is freely adjustable via a thread by which the first and the second valve core parts (1, 2) are interconnected, and wherein a defined releasable connection is provided between the first and the second valve core parts (1, 2). -- one intake opening (3a, 3b) for each of the fluids -- an outlet opening for the mixed fluid, -- an adjustment device for adjusting the temperature of the mixed fluid and -- a control element, said element having --- a thermostatic temperature sensor and --- a valve body, ---- which valve body is axially displaceable in the valve core for adjusting the inlet openings (3a, 3b) for the fluids, ---- acts against the force of a return spring and ---- is arranged between valve seats (8, 9) which are provided on the valve core, --- a thermostatic temperature sensor and --- a valve body, ---- which valve body is axially displaceable in the valve core for adjusting the inlet openings (3a, 3b) for the fluids, ---- acts against the force of a return spring and ---- is arranged between valve seats (8, 9) which are provided on the valve core, ---- which valve body is axially displaceable in the valve core for adjusting the inlet openings (3a, 3b) for the fluids, ---- acts against the force of a return spring and ---- is arranged between valve seats (8, 9) which are provided on the valve core,