Sounds like the batteries are low.
If not, do an ice bath and/or boiling water test:
Performing an Ice Bath Test
An ice bath test is the easiest way to test the accuracy of any thermometer, but only if it is created properly.
Internet videos notwithstanding, an ice bath is NOT just a glass of Ice water.!
Follow this four step process carefully to create a proper ice bath:
Step 1: Fill a large glass to the very top with ice (crushed ice is preferred but not required).
Step 2: Slowly add very cold water until the water reaches about one half inch (1 centimeter) below the top of the ice.
Note: If the ice floats up off the very bottom of the glass at all, the ice bath may be warmer than 32°F (0°C). Pour off any excess water.
Step 3: Gently stir the ice mixture and let it sit for a minute or two.
Step 4: Insert the probe of the thermometer being tested about 2 inches (5 centimeters) into the ice mixture and gently stir while you take your reading.
*In our experience, an improperly made ice bath can be off the ice point as much as 15°F (8°C).
Note: Be sure to keep stirring gently. If the tip of your thermometer probe comes to rest against a chunk of ice, it will show a temperature below the ice point and if it comes to rest against the sides or bottom of the glass, it may read higher. Your thermometer will continue to drop till it reads close to 32°F.
Performing a Boiling Water Test
Boiling water tests are even trickier to perform correctly than ice baths. Water boils at 212°F (100°C) at sea level but only at sea level. The change in atmospheric pressure at elevations above or below sea level alters the temperature at which water boils. We provide a Boiling Point Calculator that will walk you through the steps to know what the current temperature of boiling water is at your location.
You can find the online calculator at
www.thermoworks.com/boilingpointcalculator.
Once you have the target temperature written down, you are ready to begin your boiling water test:
Place 4 inches of water on the stove top, once a rolling boil begins insert the probe 2 inches down. The read out will rise until it reaches close to the temperature given to you by the calculator.
If your thermometer is reading correctly in either or both of these tests it will also be accurate over its entire range of temperatures in any food or liquid.
