Thermostatic and pressure balance valves both maintain a consistent water temperature, but they do so differently. Thermostatic valves use a wax-filled element that expands and contracts with temperature changes, adjusting the hot and cold water flow to maintain the desired temperature. Pressure balance valves use a diaphragm to adjust the water flow based on pressure changes, ensuring that the water temperature remains consistent even when the water pressure fluctuates. Thermostatic valves generally provide more precise temperature control, while pressure balance valves are more affordable and easier to install.