A burner for a heat generator comprises a swirl generator (1) for a combustion-air flow and means for injecting fuel for producing a main flow (6). A combustion chamber (2) is arranged downstream of the burner.A cavity (3) is arranged between the swirl generator (1) and the combustion chamber (2), in which cavity (3) a secondary flow (10) can be produced, and this secondary flow (10) encloses the main flow (6).