Abstract: The invention provides a thermostatic mixing valve for use within a water discharge fixture. The mixing valve comprises a cover defining an interior region, a stationary lower disk residing within the interior region, and a moveable upper disk. The lower and upper disks each have a central opening and at least one peripheral groove, wherein the grooves are alignable to form a peripheral water outlet. The mixing valve also includes a spindle assembly extending through the cover region and operably connected to the upper disk to enable alignment of the grooves and formation of the water outlet. A pressure relief cavity is formed between the spindle assembly and the cover, and wherein water flows through an opening in the spindle assembly and into the relief cavity.