Abstract: A boiler of the type having a convection enclosure with convection surfaces in which the convection enclosure is partially enclosed by walls which form a downwardly closed water-tight container. These walls extend downwardly to at least the upper portion of the convection enclosure. Inlet and outlet piping and valves are provided for the water-tight container to permit the container to be filled with water for dissolving soot and other deposits on the convection surfaces in order to clear the surfaces and to remove the contaminated water from the water-tight container. The inlet piping is equpped with nozzles located above the convection enclosure to distribute the rinsing water on the convection surfaces. Chemicals may be mixed with the rinsing water for the purpose of neutralizing the contaminated water prior to removal.