A housing unit (22) for a heating device with two heating circuits, one for space heating and another for service water heating, includes a pump housing (23) for a recirculation pump (8). The housing unit (22) encompasses a switching valve for switching the heating circuits, and in its rear installation position exhibits at least one port to directly connect a plate heat exchanger (6) for heating service water. An opening (29) for the return of the space heater is arranged on one side of the housing unit. The housing unit incorporates an inlet chamber (28), which is adjoined by the inlet mouth (26) of the pump (8), and into which two channels empty, of which one or the other can be optionally closed by a valve body (32), and of which one channel leads to the line port (30) for the return, and the other channel leads to a port of the plate heat exchanger (6).