Martin Harran wrote:
Two of my radiators have to be bled about every two weeks, the rest
are fine. I can't figure out how the air is getting into them. Any
suggestions?

it isn't air, it's hydrogen and it's being produced because you don't
have any inhibitor in the system. drain the system, add a propretory
system cleaner, leave it in for a few weeks, drain the system and
refill after dosing the system with an inhibitor.