Abstract: A fitting housing device which is to be equipped with a thermostat-controlled mixing valve (15) and a combined shutoff and reflux valve (21) for connection in a cold water inlet pipe and hot water outlet pipe of a water heater, where the fitting housing (1) has two channels (8, 10) for cold water and hot water, respectively, and a cross connection (27) for cold blending water therebetween. A mixing valve (15) is arranged in the hot water channel (8). The mixing valve (15) is connected to a regulating spindle (16), which is arranged in a first spindle bore (12). The spindle of the shutoff and reflux valve (21) can be arranged in a second spindle bore (11). The first spindle bore (12) and the second spindle bore (11) are designed such that the mixing valve (15) and the shutoff and reflux valve (21) are interchangeable relative to one another, to allow the use of the same valve housing (1) in fittings for mounting in the top, bottom and side of the hot water tank.