Revision set air vent

FB

After refilling our Buderus GB142 boiler system, the temperature difference between the supply and safety sensors displayed 2F and shut off the fire after a few seconds. The circulators were running but water for the rads was not being heated. Increasing the DHW dial setting caused the boiler to prioritize heating the coil in the Superstore tank. This resulted in much swooshing of boiler water and did not cause the fire to shut off. After playing with this back and forth prioritizing for close to an hour, the fire finally remained stable and we had hot water to the rads; the system has been working fine for over 24 hours. With all the water fall noises in the boiler each time we switched modes, trapped air seemed a likely problem. The boiler is in the basement; the rads are upstairs on the first and only floor. I had bled air from all the radiators at least three times. At the top upper left of the boiler, there is a device described in the manual as "Revision set air vent." This is located under a small removable cover that is part of the larger removable boiler enclosure. Is this air vent something that can be manually manipulated to release trapped air? If it is strictly automatic, is there a way to test it to verify it functions?
Fred in Lakewood, Colorado

Ironman

Fred,
There's a small cap on the air vent that needs to be opened about one turn. I'd leave it that way for a couple of days, or until it seams like the air is vented from the heat exchanger, and then close it.
Is there an MBR (air separator) on the system? If so, and if it has a cap, that needs to be left open.
Why was the boiler drained?

FB

Thanks for the informed answer. The system does have a Spirovent that blows like a tea kettle when it gets a big slug of air. But removing air from the actual boiler has been a challenge. We'd circulated a cleaner and had to drain and flush prior to adding the ProTek inhibitor.
Fred