A control valve for selectively regulating a fluid flow to a device, such as a heating or cooling convector, said control valve comprising: a first inlet adapted to be connected to a first fluid source; a second inlet adapted to be connected to a second fluid source; an outlet adapted to be connected to the device; an inlet selection element arranged downstream of the first and the second inlets (101, 102) and upstream of the outlet, wherein said inlet selection element is moveable between a first position in which the first inlet is in fluid communication with the outlet and a second position in which the second inlet is in fluid communication with the outlet; characterised by further comprising: a regulator cavity adapted to accommodate a differential pressure regulator, said regulator cavity being arranged downstream of the inlet selection element and upstream of the outlet; a first fluid passage in fluid communication with the first inlet; and a second fluid passage in fluid communication with the second inlet, wherein the first fluid passage is in fluid communication with the regulator cavity when the inlet selection element connects the first inlet to the outlet and the second fluid passage is in fluid communication with the regulator cavity when the inlet selection element connects the second inlet to the outlet, whereby, when a differential pressure regulator is located in said regulator cavity, a constant differential pressure can be maintained across said inlet selection element. a first inlet adapted to be connected to a first fluid source; a second inlet adapted to be connected to a second fluid source; an outlet adapted to be connected to the device; an inlet selection element arranged downstream of the first and the second inlets (101, 102) and upstream of the outlet, wherein said inlet selection element is moveable between a first position in which the first inlet is in fluid communication with the outlet and a second position in which the second inlet is in fluid communication with the outlet; characterised by further comprising: a regulator cavity adapted to accommodate a differential pressure regulator, said regulator cavity being arranged downstream of the inlet selection element and upstream of the outlet; a first fluid passage in fluid communication with the first inlet; and a second fluid passage in fluid communication with the second inlet, a regulator cavity adapted to accommodate a differential pressure regulator, said regulator cavity being arranged downstream of the inlet selection element and upstream of the outlet; a first fluid passage in fluid communication with the first inlet; and a second fluid passage in fluid communication with the second inlet, wherein the first fluid passage is in fluid communication with the regulator cavity when the inlet selection element connects the first inlet to the outlet and the second fluid passage is in fluid communication with the regulator cavity when the inlet selection element connects the second inlet to the outlet, whereby, when a differential pressure regulator is located in said regulator cavity, a constant differential pressure can be maintained across said inlet selection element.