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". Where the word boiler is used, it needs to be read as the boiler including its connecting ducts, ducts and terminals, if any. This European Standard covers gas-fired central heating boilers from the types C1 up to C9 and the types B2, B3 and B5, according to the classification in CEN/TR 1749:2009: a) that have a nominal heat input (on the basis of net calorific value) not exceeding 1000 kW; b) that use one or more combustible gases of the three gas families at the pressures stated in EN 437; c) where the temperature of the heat transfer fluid does not exceed 105 °C during normal operation; d) where the maximum operating pressure in the water circuit does not exceed 6 bar; e) which may or may not give rise to condensation under certain circumstances; f) which are declared in the installation instructions to be either a "condensing" boiler or a "low temperature boiler" or a "standard boiler"; if no declaration is given the boiler is to be considered a "standard boiler"; g) which are intended to be installed either indoors or outdoors in a partially protected place; h) which may include the facility to produce hot water, either by the instantaneous or storage principle, the whole being marketed as a single unit; i) which are designed for either sealed water systems or for open water systems; j) which are either modular boilers, or non-modular boilers. This European Standard provides requirements for boilers with known constructions. For boilers with any alternative constructions, which might not fully be covered by this standard, the risk associated with this alternative construction needs to be assessed. An example of an assessment methodology, based upon risk assessment and which covers the essential requirements of the Gas Appliance Directive, is given in Clause 11. This European Standard does not cover all the requirements for: k) Appliances that are intended to be connected to gas grids where the quality of the distributed gas is likely to vary to a large extent over the lifetime of the appliance (see Annex DD); l) Appliances using flue dampers; m) Appliances of the types B21, B31, B51, C21, C41, C51, C61, C71 and C81; n) C7 appliances that have a nominal heat input (on the basis of net calorific value) exceeding 70 kW; o) Appliances incorporating flexible plastic flue liners; p) Appliances designed to become connected to a combined flue duct system that is designed to operate under overpressure (for example Ca)); q) Appliances incorporating a combined combustion products circuit that is designed to operate under overpressure (for example Cb)); r) Appliances intended to be connected to a (common) flue having mechanical extraction.