Abstract: A fluid flow control system has a heating device for heating a fluid and a first flow path for providing the heated fluid from the heating device to a use region. A heat exchanger has a supply path that received fluid from a fluid supply, and an outlet path that receives fluid from the use region, whereby the fluid in the supply path is pre-heated by the fluid in the outlet path. A second flow path provides pre-heated fluid from the supply path of the heat exchanger to the heating device. Modulating devices control fluid flow through the outlet path along the supply path. A flow control device controls the modulating devices such that the fluid flow rates in the fluid supply path and outlet path of the heat exchanger are balanced, so as to be substantially the same.