Here is my thermometer one morning on yogurt making day; this is a day during which I desperately needed my thermometer to work. See this? That is my thermometer registering 103 degrees. Please to notice the probe is sitting on the counter. This. Is. Not. Good. After a lot of quality time with Google, I came to the conclusion that the likely problem was water in the probe; completely immersing the probe in water to wash it gets water in places it’s not meant to be. The solutions suggested were either boiling the probe in peanut oil for half an hour, or baking it in the oven at 300 degrees for half an hour, either of which should theoretically evaporate any water in the probe and render it useful again. The oven appearing to be the safest, least smoky option, I baked it. Slapped it right on the rack in the toaster oven at 300 degrees and let it cook for about half an hour. Voila, problem solved!
Update: a month later this is still working great. This is definitely a fix.