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: NOTE For further background information on appliance types see CEN/TR 1749:2014. a) that have a nominal heat input (on the basis of net calorific value) not exceeding 1 000 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.