New pool, turned on the equipment the first time Fri, May 10. All ran fine; circulated pool/spa together, pool alone, spa alone, etc. No detectable equipment problems at all. Ran the Intelliflo VS mostly on 2350 or 3450 as I tried out different water effects, skimmer efficiency, and manual vacuuming.
Tuesday, 5/21, I came home to find the spa about a foot low, and pool full (it was overflowing, but difficult to know that at the time due to massive rains that had hit that day.)
When the plasterers were here they were short one eyeball, and one of the return lines was leaking when they cut the plumbing open so they had a plug in that line. Also, the blower had never been installed, and the blower pipe was capped off. On Monday 5/20 the builder came by, removed the plug and put the eyeball on; cut the blower pipe and sat the blower on the pipe. These were the only 2 modifications to the system from when it was operating properly.
The return jet in question is in the pool, and is supposed to be plumbed in line with 3 other returns to the pool. In addition, the pool has a single, plumbed to the pad, return jet for a pressure cleaner, but is being used as a return jet. All this plumbing is 1.5". Two skimmers, and a double main drain are each plumbed directly to the pad in 2". There is also a separate 1.5 line that serves 2 bubblers, but it has been turned off.
A single 2" return line runs to the spa with 6 return jets. A 2" suction line and 2" air line also serve the spa. Spa spills over into the pool. No automation system.
As previously stated, on Mon (late afternoon) the plug was replaced with the eyeball, and the air line cut open and blower sat on. The blower was ran for a few minutes while equip was running. Early Tues morning I noticed the stone waterfall/ spillover from the spa was dry, went out to check the equip and saw that it was running, with water in the pump basket. It was still showing to be at 2350, but the suction and return was very weak (I checked the skimmer and return jet closest to the pad) so I shut off and turned the pump back on- waterfall began again, suction/return was back up and everything appeared to be working fine.
Fast forward to 8 pm, returned home to find the spa about 1" low, and pool overflowing. Equip on, valves all set where I left them- suction 100% from pool (both skimmers and main drain open), return ~60% pool/ 40% spa, all jets in pool open, bubblers on beach closed. BUT pump is behaving the same as that morning- indicating running at 2350, water in basket, but virtually no detectible suction from the closest skimmer, and very, very slight return pressure from the closest return jet (which happens to be the one that had been plugged.)
Shut off equipment and begin adding water to spa, but discover after a period of time that the water is ending up in pool. The water level in the spa is at the jets and won't go above them. Having the thought that maybe the check valve is bad, I set the return valves to spa off. The spa now begins to fill and no more water flows into pool.
Builder comes by a couple days later (system has been off) and puts the plug back into the 'offending' return jet. He sees no visible problem with the check valve. I open up valves, 60/40 return to pool/spa, but leave equip off. Spa holds water for 4 hours. Turn equip on, run for 9 hours, everything holds. Next day I remove the plug in pool jet, and spa holds water both with the equip off and on. So, I have not duplicated the problem, which leaves me quite uneasy as to when it might rear its ugly head again.
Anyone have any thoughts as to what could be going on? Or any tests I could run? Although the check valve seems to be the logical answer, what about the odd behavior on the pump, could a failing check valve cause it to behave that way? The spa drains have been set to OFF the entire time, so it seems that the water had to be coming from the spa jets, but with the pump on I don't understand how that could be- water should be running the other direction. Plus, when I turned the spa return valve to OFF, the spa stopped backflowing into the pool (pump was off at that time), which again points to the issue being in the spa return jets. Again, no automation, so nothing accidentally opening.
Here's a drawing of how the plumbing is run. The return jet locations are indicated by a colored circle on the coping. The orange jet is the jet that initially had the plug, it should be plumbed in line with the red jets. I do not have the lines terminating at the right place at the equip pad, and the cross-overs, etc are probably not exactly right. The only 2 thoughts I have come up with are an intermittently bad check valve, and a plumbing line that got connected wrong.