Abstract: A jet pump, in particular for hot-water heating systems or water-heating systems with return-flow mixing has a feeder head which is connected with a housing containing the receptor nozzle 13. The housing (7) contains a mixing tube (14) which is connected via a diffuser if needed with a second line connection (12), is coaxial with an injector nozzle (10) and adjoins the receptor nozzle (13); the mixing tube (14) also extends longitudinally through a chamber (22) of the housing in which at least a third line connection (18) and, if desired, a fourth line connection (19), directed respectively transversely to the mixing tube, discharges.In order to attain, e.g.