Any gas boiler, steam boiler or furnace that uses natural gas should be fitted with a gas train that meets either BS EN 676: Forced draught burners for gaseous fuels, or EN 746-2 Industrial thermoprocessing equipment - Safety requirements for combustion and fuel handling systems or equivalent, depending on the use. Testing requirements for these boilers depend on the components and type of your gas train.
If you are the owner of such a boiler (including a dual fuel-gas firing boiler), you need prior approval from MOM before you can install or modify.
As part of your application for approval, you will need to submit a detailed piping and instrumentation diagram of the gas train, including a full legend.