Abstract: A separable combinaton boiler comprising:a boiler body consisting of at least two horizontally aligned cylindrical boiler units each of which has in each end wall a central opening and a gas port above the central opening for the passage of combustion gases, and a front cover plate and a rear cover plate which are laid over the central opening in the front end wall of the foremost boiler unit and the central opening in the rear end wall of the rearmost boiler unit respectively, said boiler units and front and rear cover plates being separably joined together by fastening means provided thereon;a heat exchanger contained within said boiler body and divided by said boiler units into an equal number of heat exchanging elements which are interconnected by tubes to allow an uninterrupted flow of heat-transfer medium therethrough;a burner mounted on said front cover plate with its flame spout extending through a central opening in the front cover plate and the central opening in the front end wall of the foremost b