Electric boiler

An electric boiler comprising a plurality of heating element cartridges that are each substantially cylindrical in one or more inner containers that are each thermally conductive, at least one inner container surrounding one or more heating element cartridges of the plurality of heating element cartridges to define an inner passage about the one or more heating element cartridges, the at least one inner container having an inlet and an outlet for a flow of water and being arranged such as to cause water received at the inner container inlet to flow along the inner passage, in close proximity to a surface of the one or more heating element cartridges to the inner container outlet, the electric boiler further comprising an outer container in which the at least one inner container is substantially located, the outer container defining an outer passage extending around at least part of the at least one inner container, the outer container having an inlet and at least one outlet for a flow of water, wherein the at least one outer container outlet is connected to, or forms, at least one inner container inlet, wherein the outer container is arranged such as to cause water received at the outer container inlet to flow along the outer passage in close proximity to a surface of the at least one inner container to the at least one outer container outlet, and wherein the at least one inner container is shaped to have an inner surface that at least in part follows the profile of an outer surface of at least one heating element cartridge, to define at least one partly confined portion of the inner passage for water to flow between the at least one inner container and the at least one heating element cartridge, wherein the plurality of heating element cartridges are arranged in a cylindrical pattern with the outer surface of the one or more inner containers defining a continuous inner wall of the outer container.