A liquid temperature regulating valve including: a valve body having a cavity in which mixing of liquids can occur; the valve body being provided with: a hot liquid inlet adapted for communication with a source of hot liquid and through which hot liquid can enter the cavity; a return liquid inlet adapted for communication with an apparatus that uses heated liquid for heating and through which cooled liquid from the apparatus that has used heated liquid for heating can enter the cavity; a heated liquid outlet adapted for communication with an apparatus that uses heated liquid for heating and through which heated liquid can leave the cavity and flow to the apparatus that uses the heated liquid for heating; and a return outlet adapted for communication with the source of hot liquid and through which cooled liquid can leave the cavity and flow to the source of hot liquid, all inlets and outlets also being in communication with the cavity, that communication being controlled by a generally cylindrical hollow piston provided within the cavity, characterised in said piston: being associated with sealing rings that are capable of entering into sealing relationships with an inner surface of the cavity; being provided with a plurality of openings, located between the sealing rings, that permit communication between: the hot liquid inlet and an internal channel provided within the piston; and the return liquid inlet and the internal channel provided within the piston, as the piston assumes various positions within the cavity; and being movable between a plurality of extreme limits of positions within the cavity under the influence of temperature reactive means and/or manually operable temperature adjustment means; and wherein the hot liquid inlet and the return liquid inlet being in close proximity to promote the mixing of the two streams of liquid flowing into the cavity via the hot liquid inlet and return liquid inlet as the two streams of liquid flow through the internal channel in the piston from the said inlets (16, 18) toward the heated liquid outlet. a valve body having a cavity in which mixing of liquids can occur; the valve body being provided with: a hot liquid inlet adapted for communication with a source of hot liquid and through which hot liquid can enter the cavity; a return liquid inlet adapted for communication with an apparatus that uses heated liquid for heating and through which cooled liquid from the apparatus that has used heated liquid for heating can enter the cavity; a heated liquid outlet adapted for communication with an apparatus that uses heated liquid for heating and through which heated liquid can leave the cavity and flow to the apparatus that uses the heated liquid for heating; and a return outlet adapted for communication with the source of hot liquid and through which cooled liquid can leave the cavity and flow to the source of hot liquid, a hot liquid inlet adapted for communication with a source of hot liquid and through which hot liquid can enter the cavity; a return liquid inlet adapted for communication with an apparatus that uses heated liquid for heating and through which cooled liquid from the apparatus that has used heated liquid for heating can enter the cavity; a heated liquid outlet adapted for communication with an apparatus that uses heated liquid for heating and through which heated liquid can leave the cavity and flow to the apparatus that uses the heated liquid for heating; and a return outlet adapted for communication with the source of hot liquid and through which cooled liquid can leave the cavity and flow to the source of hot liquid, all inlets and outlets also being in communication with the cavity, that communication being controlled by a generally cylindrical hollow piston provided within the cavity, characterised in said piston: being associated with sealing rings that are capable of entering into sealing relationships with an inner surface of the cavity; being provided with a plurality of openings, located between the sealing rings, that permit communication between: the hot liquid inlet and an internal channel provided within the piston; and the return liquid inlet and the internal channel provided within the piston, as the piston assumes various positions within the cavity; and being movable between a plurality of extreme limits of positions within the cavity under the influence of temperature reactive means and/or manually operable temperature adjustment means; and being associated with sealing rings that are capable of entering into sealing relationships with an inner surface of the cavity; being provided with a plurality of openings, located between the sealing rings, that permit communication between: the hot liquid inlet and an internal channel provided within the piston; and the return liquid inlet and the internal channel provided within the piston, as the piston assumes various positions within the cavity; and the hot liquid inlet and an internal channel provided within the piston; and the return liquid inlet and the internal channel provided within the piston, as the piston assumes various positions within the cavity; and being movable between a plurality of extreme limits of positions within the cavity under the influence of temperature reactive means and/or manually operable temperature adjustment means; and wherein the hot liquid inlet and the return liquid inlet being in close proximity to promote the mixing of the two streams of liquid flowing into the cavity via the hot liquid inlet and return liquid inlet as the two streams of liquid flow through the internal channel in the piston from the said inlets (16, 18) toward the heated liquid outlet.