I have found that the short probes with attached dial thermometers, such as those used for frothing milk, tend to pick up steam and contaminants after only a few uses, and become not only difficult to sterilize (due to water collecting in the dial area along with contaminants), but difficult to read. Maybe mine was poorly sealed.
I recently got a temperature probe on a long cord, attached to a digital thermometer meters away from the measuring probe. It works, but I haven't had it long enough to recommend it.