The stability of 12 commercial carbon resistance thermometers has been tested at three temperatures, 12.6, 20.3, and 30 K, when the sensors were exposed to cycling between 12.6 and 293 K. The resistances of the thermometers changed markedly over 20 such cycles by amounts equivalent to temperature changes of between 0.07 and 0.57 K at 20.3 K. Both abrupt and gradual changes were observed. A few measurements were made at 4.2 K to explore the correlation between changes in resistance at various temperatures. A two‐point recalibration method is shown to be accurate to 1 mK over the range 12.6 to 30 K and can be used to 4.2 K.