Abstract: The probe (10) comprises a circuit for circulating a heat-conveying fluid, between a fluid inlet (28) and a fluid outlet (34) connected to a heat pump. The circuit comprises at least two tubes (12, 14) extending in parallel, comprising a fluid admission tube (14) and a fluid return tube (12), the admission and return tubes being put into communication (24) with each other at their distal ends (18, 22). The tubes are made with a wall in common over their entire length, advantageously a wall that is isothermal. They may be engaged one inside the other (12, 14) or they may be adjoining. The assembly forms a single tubular element suitable for burying having a distal end that is free that can easily be introduced into a tunnel of small diameter that has been dug by a miniature boring machine.