A geothermal and hydrochemical anomaly has been observed in the Vittel region (Vosges, France) in the Lower Triassic sandstone aquifer. Heat-flow measurements characterize the kilometric scale of this anomaly. A synthesis of heat-flow measurements, isotopic geochemistry, and magneto-telluric measurements shows the occurrence of a hot spring under the sedimentary cover. A numerical simulation of the hydrogeological and thermal behavior of the aquifer confirms this hypothesis and allows an estimation of flow rate and temperature of the hot spring. Finally, serious reserves are raised about the validity of beat-flow measurements in sedimentary basins.