Problem finally resolved! Plumber replace anode rod at same time replaced water pump. Since the air in line was coming only from the hot supply, I pulled the rod and the air problem disappeared. Rod was covered with thick white calcium-like coating. Don't know what this is, but looked ****** and saw that this is called "outgassing". Wonder if this is because the wrong type rod installed for my water? Anyway, need to find out what rod is made of so I can try a different metal. But at least the air is gone! Would appreciate feedback if you know about this problem.
The anode rods are usually made of magnesium. They have a steel wire in the center for support as the anode erodes.
I found this white paper (PDF) from Rheem that explains the function of anode rods very well.
Though it's out of print and somewhat obsolete, well owners need to have a copy of Max and Charlotte Alth's book "Wells and Septic Systems". It has loads of good info and will help you fully understand the processes involved from start to water flow, as well as how to resolve most problems. The pump/plumbing side is the dated part, but the earth still works the same as always.
and to KD5AWS: Fb OM es 73