Abstract: A control system for providing instant hot water at a hot water tap comprising a control unit adapted to be interposed in the fluid line between the source of water supply and the hot water tap. A heating unit is also interposed in the fluid line between the control unit and the hot water tap. The heating unit includes a closed heating chamber, a pipe arranged within the chamber and comprising a portion of the fluid line between the control unit and the hot water tap. A heating means is provided within the heating chamber for heating the pipe. The control unit comprises a fluid passageway therethrough constituting a portion of the fluid line between the source of supply and the heating unit. A flapper chamber is formed in the passageway and an inlet pipe from the source of supply has an inlet end disposed within the flapper chamber. A flapper is pivotally mounted within the flapper chamber and disposed over the inlet end of the pipe when there is no water passing through the control unit.