Loud noise from Hot press Boiler when heating is turned on

Hi

I have the gas heating on a timer so for the last few weeks I have a loud noise coming from either the hot press boiler or the attic when the heating is turned on. Sounds like it could be an air bubble, but I'm unsure even on how to resolve this. Everything works heating and hot water. Anybody any ideas???

I'm not a plumber but definitely sounds like an air lock. I had something similar a while back and had to get a plumber out, he bled the system and solved it fairly quickly, but still cost €150 cash call out.

cheers I just bit the bullet and get one.