Just changed 2 rads and boiler fires up but then shuts down?

I have just changed 2 radiators and re pressurised the system to 1 bar - Baxi Bahama 100 Combi Bolier. When I 1st put the heating on I could hear a lot of water / air moving around in the boiler, the boiler would fire up for about a minute then shut down. The boiler is also doing the same for the hot water.

Please can you advise, I presume there is air somewhere within the boiler so it shuts down rather than overheat. Is it the expansion vessel, pump or heat exchanger? I would be very grateful for some feedback. Many thanks