A thermostatic mixing valve for hot and cold water has a valve member for controlling the relative proportions of hot and cold water admitted to a mixing chamber according to user selection of a desired water temperature and a thermostat responsive to the mixed water temperature to adjust the position of the valve member to maintain constant the selected water temperature. The valve member is biased by a return spring in the form of a wave spring having a plurality of turns with transverse waves configured such that adjacent turns sit peak to peak. The wave spring is strong in compression and weak in torsion allowing the ends of the spring to move laterally to accommodate any misalignment in the components of the valve.