I have a in ground pool and spa which are separated. When I turn on the pump the spa overflows. I looked at the equipment and there is a shutoff valve and check valve between the pool and spa return lines. The flow direction on the check valve goes from pool to spa. I turned the valve to the off position and the spa stops overflowing. Just up stream of these return lines is a Jandy 3 way valve and actuator. The person at my local pool store said it sounds like the 3 way valve is bad. This does not seem to explain why the problem stops when I turn the manual valve off. So to me it seems to make sense if I prevent water from flowing into the spa it would not overfill - is there another line that would allow the spa water to get back over to the pool? Appreciate any ideas.