I have a moderate size ornamental pond (approx 1,000 gallons) and recently installed a Pentair IntelliFlo VS-AU pump. I have two issues I'm trying to troubleshoot: (1) after running on slow speeds (approx 750 rpms) for 10 - 12 hours the air pocket in the pump's skimmer chamber decreases the water level to the point where the pump shuts down. At times, I can see very small air bubbles rising from the sides of the basket. My understanding is that this indicates an air link on the suction side. I have already replaced the O-Ring to the pump basket cover after lubing it with "Leslie's Pool & Spa Lube". On the suction side the intake opening in the pond is well below the water level. I use 2" ABS from the intake to the pump. The only interruption is with a check valve connected with unions on each side and having a clear chamber. There is no sign of any air bubbles in the check valve chamber. The suction pipe then connects to the intake port on the pump. There are no leaks on the suction side or at the drain plugs. To eliminate the air leak I plan on redoing all of the connections this weekend. My question is, in addition to lubing the O-rings, what is the preferred sealant to use on the threaded side of the unions - teflon tape or silicon lube? In addition should I do anything else on the female side of the pump's intake port? I will also replace the teflon tape on the drain plugs. I ask because the gentleman at the pool store recommended I use a "Boss 315" silicone jelly on the pump's intake port and I wondered whether this is preferred over teflon tape.
(2) My second question concerns the pump's low water shut down protection. When the water level in the pump basket gets too low, the pump trips the circuit breaker at the subpanel without simply going into a "stopped" state and indicating a low water alarm on the control panel. This is contrary to my understanding that the pump, when it senses insufficient water, should issue an alarm indicator and go into a "stopped" state without killing the power. The pump runs on a dedicated circuit, all wired in accordance with instructions. Any advice on why the pump's protective system is not working?
Thank you very much for your time, and all suggestions are welcome.