Watkins Pressure Switch 73995 Fits Various Caldera & Hotspring/HotSpot Spas Part Number: 73995 Pressure switch compatible with various Caldera & HotSpring/HotSpots spas. The pressure switch is a safety device designed to prevent overheating of the spa heater should a low or no-flow condition exist in the spa. The pressure switch is located in the heater circuit. When the switch is closed (proper flow), voltage is transferred to the heater circuit when the control thermostat calls for heat. Hot Spring Spa Supplies carries spa fragrances, air & water valves, control systems, filter accessories, lights, cleaners, pumps, thermostats, and more for virtually every hot spring model.