Air lock in boiler return pipe

[Rosscardwell]

I have a issue which I’m assuming is an airlock in the return pipe just above the boiler. The pipes go up and over and then enter the boiler at the bottom. The boiler fires up normally but the heat doesn’t get far and the the pipes next to the boiler make like a fluffing noise. I’m not the most experienced DIY plumber but have taught myself the basics. So what I think is happening is the water is trying to go up the return pipes, it cannot get passed the trapped air so the boiler shuts down and the heat doesn’t make it to any rads. Ive bled all rads and no air. Ive tried just hot water to force it through but same issue. I’m he boiler is in the bathroom close to a rad so I tried to force the air down to the rad but I can’t get it out. I would appreciate some advice if any on how to shift it?
The pipes only get hot to just before the pump. Ive attached a photo of the pipes at the boiler. Am I right thinking this is a perfect spot for an airlock and should have a AAV on there? Is there any other way to shift it?
Many thanks