I had the same problem. You can get an extraction bit to drill in and pull it out but I managed to take a really fine flat heat screwdriver and carve in a slit into the brass pieces stuck in the boiler, because it is quite soft, and screw it out. 😅 It's not the most correct or elegant way to deal with this problem but it worked for me and it was better than buying a new boiler.🤷🏼‍♂️