Abstract: The boiler, which is of the wall-mounting kind, comprises: a burner connected to a gas supply part; a combustion chamber; a heat exchanger; distribution, exchange and control components and communicating passages between them; inlet and outlet lines connected to the exchanger; and external connections. The distribution, exchange and control components are combined on a common mounting plate which comprises some of the functional elements of each component and in which the connecting passages for each component extend, such passages being in the form of internal passages in the mounting plate. Of use for facilitating assembly and maintenance and reducing the risk of leakages.