Spa water siphoning to pool?

[normanzoo]

Hello, hoping I can find some help here, I feel like we're fighting a losing battle with our pool and spa. After recent rains, we had a lot of debris end up in our pool, and we've spent the last 2 weeks doing nothing but filter cleaning, backwashing, and finding new problems with equipment. We have a Pentair DE filter with backwash and a salt system. We had a new pump and salt converter installed in January, and just had a new backwash valve put in after so much pressure in the filter kept pushing the pin up so hard on the backwash valve it would break the plastic piece holding the pin down. We were unable to remove the value ourselves, and apparently the bottom O ring had gotten glued down. Now we are having the problem that whenever the pump is turned off, the water in the spa siphons down to a certain level each time and puts all that water into the pool. Each time this happens it pushes the pool water level above the drain and we have to keep adding water. It seems that the actuators for the spa are working fine, can anyone point us in a direction to start looking? What should we be testing to try and narrow down the problem? We're unsure if this started happening after the backwash valve was repaired or after a seal on the salt converter was repaired as that was within 1 day of each other.

Thanks in advance for any help!
Linda

[deja-blue]

Your check valve is bad. This is letting spa drain back into pool.

[deja blue]

depending on what type of check valve it is you might be able to just buy the guts or a rebuild kit,and not have to actually change the whole check valve.