Abstract: A gas fired direct contact water heater in which the heated water is led off from a reservoir in a lower part of the heater through an outlet conduit including a continuously running pump pumping the heated water along the conduit to a user's valve which is opened when the user requires heated water. To replace that water a water supply conduit controlled by a ball-cock valve conveys water to a first spray bar in an upper part of the heater above heat transfer means through which passes the downward flowing water and upward flowing products of combustion resultant from the burning fuel gas. A return conduit opens into the outlet conduit between the user's valve and the pump. The return conduit leads to a second spray bar in the heater above the heat transfer means.