This European Standard applies to boilers used for central heating (heating boilers) with forced draught burners with a nominal heat output not exceeding 1 000 kW, which are operated either with negative pressure (natural draught boilers) or with positive pressure (pressurized boiler) in the combustion chamber, in accordance with the boiler manufacturer s instruction. This standard specifies the necessary terminology, the requirements on the materials and testing of them, and marking requirements for heating boilers. Particular requirements for boilers that can be used with open vented systems are contained in EN 303-4. The requirements of this standard apply to heating boilers that are tested on an authorized test rig. Boilers in accordance with this standard are designed for the heating of central heating installations in which the heat carrier is water, and the maximum allowable operating temperature of which is restricted to 100 °C. The maximum allowable operating pressure is 8 bar. For boilers (storage or continuous flow heater) this standard only applies to the parts of the water heater that are necessarily subject to the operating conditions of the heating boiler (heating part). This standard does not apply to gas boilers with atmospheric burners, boilers for solid fuels, boilers and boilers with oil vaporization burners. For these boilers there are further requirements.