Upon arrival customer stated the heating pipes are making loud banging noise when the heat is running. Turned both thermostats on and went to the boiler. When the boiler was running we heard pockets of air inside the pipes. Also found a hi-vent on the second floor zone had been leaking at some point in the past and had corrosion running down the side of it. After getting customer authorization we drained pressure from the system and removed the old hi-vent. Installed a new hi-vent and filled the system back up with water. Bled air from both zones. Started and tested the system. Had hot water coming back on both returns and did not hear any air remaining in the system. When leaving the system pressure was at 20psi. System is operating properly