Shall be according to EN 15502-2-1:2022, Clause 1 with the following modifications: Add at the end of the list, after k), following: This document covers gas-fired central heating boilers from the types C1 up to C(11) and the types B2, B3 and B5 : l) which are fully premixed appliances equipped with an Adaptive Combustion Control Function (ACCF) 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 including gas grids for natural gases of the second family where up to 20 mol% H2 is added to the natural gas (H2NG-Y20). m) which are fully premixed appliances equipped with a Pneumatic Gas/Air Ratio controller (PGAR) that are intended to be connected to gas grids for natural gases of the second family where up to 20 mol% H2 is added to the natural gas (H2NG-Y20), where the quality of the distributed gas without adding the hydrogen is not likely to vary to a large extent over the lifetime of the appliance. Replace in the list following This document does not cover all the requirements for : ab) and ak) and al) by: ab) 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 AB of EN 15502-1:2021), except for fully premixed appliances with an ACCF, as ACCF appliances are designed to adapt to variations in gas quality. ak) appliances that are intended to burn natural gases of the second family where hydrogen is added to the natural gas, except for fully premixed appliances with an ACCF or PGAR (which are covered by this document); al) Partially premixed appliances equipped with an adaptive combustion control function (ACCF).