The invention relates to a furnace (10) for heating preforms (20), of the
type that comprises a preform-heating tunnel (12). According to the
invention, the tunnel consists of a heating module (18) comprising
vertical walls (14, 16) between which the preforms (20) travel. Moreover,
at least one wall (16) of the module (18) is provided with at least one
heating means (32) which is mounted to supports (34) such that it can
move transversely and means (40) for adjusting the transverse position of
the heating means (32) comprising at least one member (42) for
controlling the movement of the heating means (32) between at least two
indexed positions. The invention is characterized in that the control
member (42) comprises an indexing boss (54) which can deform elastically
such as to fit inside the complementary indexing notches (56, 58) on the
corresponding support (34) at proximal and distal positions respectively.