PURPOSE: To contrive maintanance, easiness in cleaning and miniaturization of the titled boiler, by constituting the titled boiler by making a water tube group and fire tube group into paths which are independent of each other, making the water tube group into a unit attachably and detachably by part of the same and combining a fire tube type, water tube type and flow through type boilers with one another, in the boiler using solid fuel such as a small chip of wood.

CONSTITUTION: A flow through type water tube group 3 of a water tube group 8 composed of a stationary water tube group 6 constituting one path mesh and a main header 7 is arranged on the upper part of a boiler. Then two path mesh is constituted of a boiler shell 4 and fire tube group 9 and juxtaposed with the water tube group 3. A top and bottom branch headers 10 are fixed to a plate 11 of the side of the boiler with a bolt by making the headers 10 into a unit. Maintenance and cleaning of the titled boiler becomes easy by a method wherein each part is made into a unit and is made detachable and attachable.