Chlorinator Issue

[FWPOOL]

Hello,

Looking for some help with a Pentair 320 chlorinator. When the equipment shuts off it bleeds out all of the water, leaving the tablets in a vapor lock. The pot on the pump does not loose prime nor do I get air in the DE filter so the suction side appears to be ok. Any thoughts where the issue could be on the return side? The flow goes through a heater, past a check valve (assuming to keep the super chlorinated water from going into the heater) then to a jandy value splitting the return to the spa / pool

Thanks