Boiler of the type in which the hydraulic circuit (2) is made by assembling elements made of cast-iron obtained by casting without a core, characterised in that said elements each constitute a complete integrally cast transverse section of the boiler delimited by a pair of concentric rings (4, 5) with a slightly frustoconical shape which are kept spaced apart by an annular bottom (7) comprising orifices (10) for circulation of water, the successive sections being assembled by screws and bolts with interposition of a gasket (8). <IMAGE>
