I have a new (old) house. When I turn on a hot water faucet, it runs for a few seconds, then it spits air for a few to several second, and then it runs normally. If left alone for an hour or two it will do the same. The longer it sits the more air it seems to collect and purge. It does not do this on the cold water side. Also, my hot water tank often burbles. If I run an impact sprinkler it seems to be related.
I looked for leaks but could not find evidence. I turnd water valve off at pump house and placed 70 pounds of pressure on the plumbing. It dropped to 64 in about 24 hours - I would think a leak would drop much more (I rationalized the 6 pound pressure loss was through a fixture). Also, I don't know how air would get in a pressurized static water system - but I am not a plumber.
I am now suspecting the pumping system. I do not know how the air would get to the house supply line, go 80 feet and get into the hotwater - especially since I have a line that goes uphill to a barn; but I guess anything is possible. Could it be getting in through the pressure tank? How about a water softener ( mine does not work (no water in the brine tank). Could air be sucked in that way? I think my pump runs OK - can't hear anything - can only tell it is runnng by watching the electric meter.
Ideas? Thank you.