We just remodeled our pool when we filled it up about 1 month ago, the spa would empty into the pool when filter was off...my husband replaced a valve and it wasn't doing it anymore, he just cleaned the filter this week and now it is doing it again. It seems to be something correlated with cleaning the filter
Pool & Spa - Water Pik - Aqualink Rs4 Package - Pool and Spa Combo
Answers & Comments
There are a number of reasons the water can drain back into the pool. It could be the backwash valve. It could also be an automated 3-way valve that is not fully going in the right position when it is in the pool mode. Sometimes a switch on an automated valve is in the wrong position. Some systems have a check valve that is not fully blocking flow in the reverse direction. Follow the path the water might be taking and it might help you figure out what it is. You may need to take one or more valves apart to make sure what position it is in and inspect the sealing surfaces. If you take a valve apart make sure you grease any o-rings or seating surfaces as you reassemble it. Good luck.