The invention relates to an apparatus for heating plastics preforms (3), having a transporting device (20) which transports the plastics preforms (3) along a predetermined transport path (TR1, TR2), having a heating device (40) which at least temporarily heats the plastics preforms (3), wherein the heating device (40) at least comprises: ⋅ - a bottom heating element (4115) which is suitable and intended for heating a bottom portion (B) of the plastics preforms (3), ⋅ - a reflector element (4113) which is fitted under the bottom portion (B) of the plastics preforms (3) in the longitudinal direction (L) of the plastics preforms (3) and reflects thermal radiation onto the plastics preforms (3), ⋅ - an adjusting device (50) which is suitable and intended for adjusting the reflector element (4113) in the longitudinal direction (L) of the plastics preforms (3), and wherein the apparatus has a control device which is suitable and intended for automatically switching at least one heating element (4110) on and/or off depending on the position (S3, S2) of the reflector element (4113) with regard to the longitudinal direction (L) of the plastics preforms (3).