Installed a new check valve (aka one-way valve). This is on the spa suction / intake side. Issue: Spa draining down when the equipment is off. Cause: Usually one or more failing check valves. These valves are designed to hold water level and only allow flow in one direction. This install is a spring-loaded check valve that works off water pressure. When water flows, it pushes the spring open. When flow stops, the spring snaps shut and prevents backflow. Simple fix. Big difference. One way valve,