The guy pressure tested it at 2 bar. He said he didn't want to go any higher just in case.The air is being sucked in via the vent so if you seal it the air wouldn’t get in also you would run it at a pressure of 1 bar not 6
you’ve said you had it pressure tested for leaks so in theory the system would be ok sealed
try turning the pump speed down to 2 it’s on 3 atm
I already turned the pump down to 2 and it made no difference. I turned it up to 3 hoping it would address the cold radiator issue I mentioned in my original post. It didn't.