Safety groups of this type are used to protect pressurised water heaters according to the requirements of DIN 4753-1 and EN 806-2. They are compact appliances which incorporate all the necessary safety devices such as check valve, shut-off valve, test point and diaphragm type safety valve in one unit. The safety valve protects the downstream cylinder, pressure vessel etc. by automatically opening when excess pressure occurs. The check valve prevents back pressure, backflow and back syphonage of water from the hot water unit.