A thermostatic mixing valve including: a first fluid inlet; a second fluid inlet; an outlet; a thermostatic element connected to a return spring and a piston such that movement of the thermostatic element assists with moving the piston, movement of the piston controlling fluid flow from the first fluid inlet and the second fluid inlet to the outlet; a housing containing an overtravel spring, the overtravel spring configured to resist a force applied by the thermostatic element during movement thereof; and a plunger extending into the housing, the plunger configured to engage the overtravel spring, wherein rotating the plunger adjusts the resistance applied onto the thermostatic element from the overtravel spring.