Spa drains back to pool

[Stu]

I changed my pool filter yesterday and when the cleaner shuts off the water in the spa drains into the pool.When the cleaner comes on the water comes back into the spa.

[Larry]

Hi Stu

It sounds like you have a problem with the check valve (one way valve/ non-return valve). If the valve is faulty, it will allow water in the elevated(?) spa to flow into the pool. When the pump runs it refills.

When you say that you changed the filter, do you mean you installed a new filter, or did you only replace the cartridges/ collectors? Did you make any changes to the plumbing too? Could something have entered the pipes causing the check valve to jam open?