The setup: pool new to me from 4-5 months ago, about 14x30 generally rectangular with elevated spa/spillover waterfall.
The problem: with the pump off, water level in the spa was dropping. The longer the pump was off, the lower it dropped, but it generally stopped right below the returns.
The suspicion: faulty check valve.
The result: I shut off the spa return, presumably that valve (which is after the check valve) would stop the water. So, with the pump off, it did get back to the previous level.
The twist: I ran the pump on the pool side only (spa return shut off), and the next morning, the spa was DRY. The pump was not fully primed. So, the problem is on the suction side. Only suction out of the spa is its drain.
The confirmation: running the pump, I stepped into the now dry spa, and could hear gurgling.
The diagnosis: faulty Jandy valve, the only way to control the spa main drain: directs suction from pool or spa, and Jandy valve on the pressure side directs returns to pool/waterfall or solely to spa.
The fix: repair/replace Jandy valve.
Is the above the right logic? Thoughts/feedback would be appreciated.
I know I am a bit late for airing this grievance. Happy (insert holiday you observe) to you!