Suction Leak Causes Pump to Run Dry

I have a 30,000 gallon in-ground. In order to maintain my prime, when I shut off my pump I close the multiport valve for the inlet that connects the skimmer line and main drain into the pump. Otherwise if the pump is off for several hours, I will lose my prime - this is the reason I cannot use my timer to operate the pump. By mistake, my pump came on when the valve was in this position and ran dry for several hours. It generated enough heat to warp the pump basket slightly.

The issue I have now is that the pump will work but when I attempt to prime the pump the skimmer side will continuously take water and never raise the water level in the basket area. This is not true of the main drain side. If I change the multiport setting to close the inlet from the skimmer, I am able to prime and raise the water level. But whenever a portion of the skimmer inlet is open I can never raise the water level. It just keeps flowing toward the pool. And I am getting air into the system that I have to bleed.

What does this mean? A leak somewhere? What is the best approach to fixing it? How could it have happened? Any help is appreciated. Thanks.

Quite possibly when the basket area heated up and warped you could have opened an air leak at either the basket lid or the pipe fitting. Don't understand why the difference in behavior between the main and skimmer ports. Almost sounds like the leak could be at the valve but I assume that part didn't get hot....unless it is hooked directly to the pump. You can try using a squirt bottle to squirt water around the suspected areas and see if it gets sucked in when the pump is running and the skimmer line selected. Can also use a piece of small diameter hose as a stethescope however the pump noise may make it difficult or impossible to hear the air leak. It also sounds like you had a leak somewhere in the system all along because of your need to close the suction valves to prevent water from draining back.
Hope this helps.
Al

I too had a similar problem, however it is difficult to understand why the operation of the multi-port valve would be sensitive to its positioning. At any rate, here's my fix.

Yes the pot became very hot, yet after removing the lid and checking the pot with a straight edge I didn't find any warping. I did replace the gasket, and used plenty of lube. Despite this effort a loss of prime still occured, hence I assessed the intake and discharge fittings.

After draining the pump, and drying the fittings with a hair dryer, I placed pvc primer and glue on the fittings and let it thoroughly dry. I wasn't too hip on glueing the fittings to the pump, however I figured the next fix would be replacing those fittings, that would be an extremely labor intensive process.

Two years later, everything works okay.