How can I fix a worcester Bosch Junior Greenstar ?

Please does anyone have any ideas about the problem with my Worcester Bosch Junior Greenstar boiler, approx 3 years old
I'm afraid to leave the heating on because of a sudden bubbling
sound... like a kettle boiling.. then the gas pilot
little green flame goes out then BANG BANG BANG... and
the light comes back on to start the process again ?