I'm still relatively new to managing a pool (~2 years). This week I had a lot of air under the clear lid to my pool pump.
Hmmm....made sure all the skimmers were clean, had plenty of water in the pool (mid-skimmer) and no blockages.
Found the article: Pool School - Suction Side Air Leaks
"1. The most common source is the pump basket lid. It must have an airtight seal. Replacing the O-ring often helps. Proper cleaning and lubrication of the O-ring with a silicone based lubricant (Magic Lube is one brand) may be necessary....do not use WD-40 or petroleum jelly. "
"Often, you can confirm this as the source by slowing pouring water over the lid (pump running) to see if that stops or minimizes the air in the basket."
As soon as I ran my hose over the lid, the air disappeared. Good, should be an easy fix. Tried taking out the existing O-ring & cleaning the lid/o-ring & replaced. Nope, same problem.
Bought a new O-Ring (official Jandy replacement part). Worked like a charm for ~1 hour. I decided to vacuum the pool. Afterwards, I always empty the skimmer & pool-pump basket. Once I replaced the lid (remember, new O-ring), I was getting air again.
Ran more water over the lid - confirmed I had a leak in one specific spot. Grabbed the silicon gel and made sure there was enough on the O-ring. Problem fixed. Not an air bubble is sight!
My total cost: $25 & a little time/effort. Saved me over $150 had I called my pool repair service.