This European Standard specifies the requirements and test methods concerning, in particular, the construction, safety, fitness for purpose, and rational use of energy, as well as the classification and marking of gas-fired central heating boilers that are fitted with atmospheric burners, fan assisted atmospheric burners or fully premixed burners, and are hereafter referred to as “boilers”. This European Standard applies to boilers of type B, as listed in 4.2: ? that use one or more combustible gases of the three gas families at the pressures stated in Tables 16 and 17; ? that have a nominal heat input (on the basis of net calorific value) exceeding 300 kW, but not exceeding 1 000 kW, including modular boilers; ? where the temperature of the heat transfer fluid does not exceed 105 °C during normal operation; ? where the maximum operating pressure in the water circuit does not exceed 6 bar; ? that can give rise to condensation under certain circumstances; ? of the standard and low-temperature types. This European Standard applies to boilers designed for sealed water systems or for open water systems. This European Standard does not contain all the requirements necessary for boilers: ? intended to be installed in the open or in living rooms; ? permanently fitted with more than one flue outlet; ? where the combustion circuit is sealed with respect to the room where the boiler is installed; ? of the condensing type; ? intended to be connected to a common flue having mechanical extraction; ? fitted with a forced draught burner in accordance with EN 676 (see EN 303-7); ? producing hot water for domestic purposes. This standard only covers type testing. Matters related to quality assurance systems, tests during production, and certificates of conformity of auxiliary devices are not dealt with in this European Standard.