Once we see the photos of your valve arrangement we can better see what the problem is but if there is no check valve I would suspect a bad valve or actuator. Try disingaging the actuators (if don't know how let us inow what brand and model of automation and actuators you have) and turining the valves manually (If you donlt know how don't do it).
Pictures of the valve positions in both pool and spa settings (or pool and spillover, however your system is set up) would be very helpful!