Heating boilers. Gas-fired central heating boilers. Assembly comprising a boiler body and a forced draught burner|Boilers, Heating equipment, Gas-powered devices, Hot-water boilers, Central heating, Hot-water central heating, Forced-draught burners, Gaseous fuels, Rated power, Equipment safety, Cut-out devices, Control equipment, Controllers, Temperature, Efficiency, Thermal efficiency, Performance, Performance testing, Acceptance (approval), Approval testing, Testing conditions, Errors, Formulae (mathematics), Combustion products, Combustion, Carbon monoxide, Instructions for use, Classification systems, Thermal testing, Temperature measurement, Heat loss, Flues, Diameter, Service pressure, Pressure control, Sampling equipment, Air