This European Standard defines the specifications and test methods concerning the construction, safety, rational use of energy and fitness for purpose, and also the classification and marking of gas-fired instantaneous water heaters for sanitary uses. This standard applies to water heaters: a) of types AAS, B11, B11BS, B12, B12BS, B13, B13BS, B14, B22, B23, B32, B33, B44, B52, B53, C11, C12, C13, C21, C22, C23, C32, C33, C42, C43, C52, C53, C62, C63, C72, C73, C82and C83; b) fitted with atmospheric burners; c) equipped with atmospheric burners assisted by a fan for the supply of combustion air or evacuation of combustion products or fully premix burners; d) using one or more combustible gases corresponding to the three gas families and at the pressures stated in accordance to EN 437; e) of nominal heat input not exceeding 70 kW; f) with an ignition burner or with direct ignition of the main burner. This European standard applies to type C water heaters as listed in accordance to Technical Report CEN/TR 1749: a) types C1, C3 and C5 water heaters including their combustion air supply and combustion products evacuation ducts and their terminal(s); b) types C2 and C4 water heaters including their connection ducts but without the shared duct system ; this shared duct system is part of the building; c) type C6 water heaters without any ducts; the ducts are separately approved and marketed; d) type C7 water heaters up to the draught diverter/air inlet but without the secondary flue; e) type C8 water heaters with their connecting ducts but without the chimney, which is part of the building. This standard only covers water heaters where the fan, if any, is an integral part of the appliance. This European Standard: a) does not apply to appliances not intended to be connected to a flue when they are not fitted with an atmosphere sensing device; b) takes account of the information given in Technical Report CEN/CR 1472 with respect to marking; c) only covers type testing.