1. A heating device configured to heat preforms made of thermoplastic material, the heating device comprising:a subassembly including a lamp having a tubular bulb and two free end segments, each of the two free end segments having an end stem of the bulb and an end base that is secured to the end stem;
at least one reflector that extends longitudinally at a set distance from the tubular bulb in a transverse direction, the reflector having a front face having a concave cross-section and configured to reflect electromagnetic radiation; and
two holding elements configured to hold the lamp in a transverse position relative to the reflector, each holding element being secured to the reflector, each of the two holding elements having an end-stop and being rigid with respect to the transverse direction, such that the transverse distance between each of the end-stops and the reflector is constant and defines the set distance,
wherein the subassembly is mounted in a removable way on each holding element by reversible interlocking of a portion of each respective one of the free end segments of the lamp with a housing of one of the holding elements, the housing having a complementary shape with respect to the portion of the respective free end segment, the reversible interlocking being in a direction that is orthogonal to the longitudinal direction, and
the subassembly having a complementary stop surface configured to contact the end-stop of the holding element to position the subassembly with respect to the reflector.