recently when showering or opening hot water supply at fixtures, im having air shoot out of showerhead or faucet for like 5 - 10 seconds. Sometimes its quite strong. How is it getting in the water lines? Ive repiped the entire house with CPVC 10 years ago.
Try opening up the refief valve on the water heater untill water goes out, then start opening up every valve starting with the closest one to the incoming water line, outside taps, flush every toilet, sink, tub and shower.
Could be as simple as one of the lines in the street has been worked on causing it.