If you have the old style air over water tank (everything in one tank), sometimes an air vent that's really good can pull the air out of there too from a long ways away in the system.
If you have a bladder tank, make sure it's still hollow sounding.
Not a whole lot that can introduce air into a system, but on the other hand, air in the system can sure make you pull your hair out.
I had a 5 story building I accidentally got some air into. You'd think it would have just settled out in the top floor... but it didn't. Seems like most of the air was in the 3rd floor, and hardly any in 5th.
"If you call that hard work, a koalas life would look heroic."
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