This document specifies, dimensions, materials and performance requirements (including methods of test) for expansion groups, of nominal sizes from DN 15 to DN 25, having working pressures1) from 0,1 MPa (1 bar) to 1,0 MPa (10 bar). Expansion groups shall be fitted to the cold potable water supply only for expansion purposes, e.g. of storage water heaters, having a maximum distribution temperature of 95 °C. Expansion groups limit pressure in the water heater to which they are fitted, that is produced by thermal expansion of the water, prevent the backflow of water into the supply pipe and prevent the discharged water to get into contact with the water in the water heater. Expansion groups do not control temperature and alone do not constitute the protection required for storage water heaters. NOTE The use of the device specified in this document does not override the need to use controls (e.g. thermostats and thermal cut-outs) which act directly on the power sources of water heaters.