A flow-through heating system (1) is described, comprising: a flow tube (11); a plurality of at least two heating elements (12A, 12B, 12C), each heating element being connected in series with a corresponding controllable switch (23 A, 23B, 23C); a control unit (30) having control outputs (33A, 33B, 33C) coupled to said controllable switches; the control unit (30) being designed to generate control signals (Sa, Sb, Sc) for opening and closing the controllable switches such that said heating system is operated at a required power (Pr) less than the power capacity (Ptot) of said heating system by operating precisely one of said heating elements at reduced power while the remaining heating elements are either operated at full power or at zero power.