Historically, anomalies with heat transport in hydrogen gas played a key role in shaping Knudsen’s rarefied gas theory. Knudsen was astonished that while his kinetic theory of gases correctly estimated momentum transport in low pressure gases, it greatly over-estimated heat transfer from a platinum wire to rarefied hydrogen and helium gas. These observations lead to the development of Knudsen’s accommodation coefficient for estimating the temperature discontinuity that occurs at the boundary between a solid surface and a gas. Such temperature ‘jumps’ are highly undesirable in equipment designed for measuring thermal conductivity of gases since they can lead to an apparatus dependent underestimate of the bulk thermal conductivity of the gas. Motivated by the potential of hydrogen as a major future energy carrier, presently at the Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), AIST / Kyushu University, Japan, we are attempting to re-measure the fundamental thermophysical and transport properties of hydrogen gas in the range of pressures from 0.1 to 100 MPa and 25 to 500°C. In designing the thermal conductivity measurement cell we arrived at the surprising result that simple slip-boundary theory predicts a non-negligible temperature jump at the surface of a 10 micrometer diameter platinum wire in hydrogen at pressures even slightly higher than atmospheric. The results of the present finding have relevance to both measurement of hydrogen thermal conductivity and to theory applied to microsensors that use the thermal conductivity as the measured physical quantity.