A method of the present disclosure is especially useful for cooling a multiplicity of processors (heat sources) in a data center or the like. As shown in FIG. 2, supply of coolant fluid is in fluid communication with each heat source or processor 3 by means of the supply manifold 7. A control valve 1 is provided for each of the processors 3, where each control valve has a housing 15 with a chamber 17 therewithin. The chamber has an inlet 9 for receiving coolant fluid from its respective processor 3 (or heat source) such that the temperature of the coolant fluid entering the chamber reflects the temperature of its respective processor and an outlet 11 for the discharge of coolant fluid from within the chamber. The control valve has a valve member 29 that is responsive to changes in the temperature of the coolant fluid within the chamber 17 to effect movement of the valve member between a closed position in which the flow of coolant fluid from within the chamber is substantially blocked and an open position enabling the flow of fluid from the chamber via the outlet 11. The method comprises a step of permitting a minimum flow of coolant fluid from within the chamber 17 of control valve 1 when the valve member is in its closed position such that a minimum flow of coolant is supplied to a respective heat source 3 when the valve member 29 is in its closed position so to supply a minimum amount of cooling to the processor when the heat output of the processor is minimal and so that the temperature of the coolant fluid entering the chamber reflects the temperature of the processor associated with the control valve. When the temperature of the coolant fluid within the chamber exceeds a predetermined first temperature T1, this temperature change effects movement of the valve member from its closed position toward its open position thereby permitting more coolant fluid to flow to its respective processor so as to maintain its respective processor within a desired range of operating temperatures.