Shall be according to EN 15502-2-1:2022+A1:2023, Clause 1 with the following modifications: Replace: This document covers gas-fired central heating boilers from the types C1 up to C(11) and the types B2, B3 and B5: By: This document covers gas-fired central heating boilers from the types C1, C3 up to C9 and the types B2, B3 and B5 : b) is replaced by: b) that use combustible gases of gas group 4Y at the nominal pressure of 20 mbar; Appliance category Pn Pmin Pmax 4th family 20 17 25 k) is not applicable. Add at the end of the list, after k), the following: l) which are fully premixed appliances equipped with a Pneumatic Gas/Air Ratio controller (PGAR) or an Adaptive Combustion Control Function (ACCF) that are intended to be connected to hydrogen gas grids where the quality of the distributed hydrogen gas is likely expected to stay within a Wobbe range of 42 to 46 MJ/m3. Replace in the list following This document does not cover all the requirements for: ab), ag), ah) and al) by: ab) appliances that are intended to be connected to gas grids where the quality of the distributed hydrogen gas is likely to vary outside the Wobbe range of 42 to 46 MJ/m3; ag) C(10) boilers; ah) C(11) boilers; al) partially premixed appliances equipped with an adaptive combustion control function (ACCF); and add an) and ao); an) the conversion from natural gas to hydrogen; ao) the risk of aeration of the gas supply to the appliance.