the water chamber including one or more fire tubes

Full Title

Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters (steam boilers F22B) > Water heaters other than continuous-flow or water-storage heaters, e.g. water heaters for central heating > with water chamber arranged adjacent to the combustion chamber or chambers, e.g. above or at side > the water chamber including one or more fire tubes