The paper deals with the leakage control and quality assurance of fabrication pressure vessels for water heating. A relevant welding device and process are described. MAG welding including the equipment for welding water-heater shell,the power source using a welding rectifier with a horizontal static characteristic and measuring welding current and arc voltage during welding are schematic represented. There are shown defects, which are most often occurred at the junctions between the longitudinal and circumferential welds and at the contact between the start and end of the circumferential weld. One part of the paper describes, how to improve the fabrication of pressure vessels for water heating by welding. Spatter free ignition (SFI) of the welding arc by MAG welding is described. Finally, a leak tightness testing of welds is represented.