[Redwood]

Some systems do not have bleeders at the high point.
On these a hose is placed on a drain by the boiler, with the circulator off, certain valves closed, and fill water is run through the system to force the air out the hose because of the high flow rate. It is probably best if you could have someone that knows what they are doing show you how to do it if you don't have bleeders.