How to release air in combi boiler?

i have a parva HE combi boiler fitted in 07. my boiler when firing up used to make a loud noise when the hot water or heating came on, i was told it was air in the system. i bled the radiators and no air was released from them. now it makes the noise of firing up but doesnt ignite leaving me with no hot water or heating. the pressure is between 1 and 2. if it is air how can i now release this from the system? many thanks