Editor’s note: Originally published May 2021. Reviewed and updated November 2026.
To reset an infrared thermometer, first confirm it actually needs it by checking it against ice water or boiling water. If it does, use the reset button if your model has one, or remove the batteries for a few minutes and reinstall them. Many problems, including blank screens and “Er” messages, turn out to be weak batteries or a dirty lens.
Quick answer
- Check accuracy first: an ice-water slurry should read about 32°F, and boiling water about 212°F at sea level (lower at higher altitudes).
- If your thermometer has a reset button, use it. If not, remove the batteries for a few minutes, reinstall them and switch it back on.
- An “Er” message on the display usually means the unit needs a reset or recalibration.
- If it won’t turn on, replace the batteries first. If it still fails, contact the manufacturer.
- Check accuracy when the thermometer is new, after it has been dropped, and at regular intervals such as once a month.
This guide answers the most common questions: how to factory reset an infrared thermometer, how to switch it to Fahrenheit, what to do when it isn’t working, and how to clear an error.
Step 1: Find out if your thermometer needs a reset
Infrared thermometers are used for cooking, industrial work and checking body temperature. Whatever the job, a thermometer that reads wrong is no use, so start by testing its accuracy. There are two common methods, and using both gives you the best picture. Our guide on how to calibrate a thermometer covers them in more depth.
Keep in mind that an infrared thermometer reads the surface it is pointed at. Aim at the water or ice itself, not at the side of the container. If you are unsure how this differs from a probe, see infrared vs probe thermometers.
Ice point method
- Fill a jar with crushed ice.
- Slowly add cold water until the ice is just covered.
- Stir the mixture.
- Wait about 10 seconds, then take a reading of the mixture.
- A reading of about 32°F (0°C) means your thermometer is working properly and doesn’t need a reset.
Boiling point method
- Use a pot or heat-safe jar and fill it so the water is around 6 inches deep when boiling (start with roughly 7.5 inches to allow for evaporation).
- Heat the water until it reaches a steady boil.
- Take the reading at the center of the water, not near the edges, where the temperature can differ slightly.
- Compare the result with the boiling point for your altitude.
Water boils at a lower temperature the higher you are above sea level. Approximate boiling points:
| Altitude | Approximate boiling point |
|---|---|
| Sea level | 212°F |
| 1,000 feet | 210°F |
| 2,000 feet | 208°F |
| 3,000 feet | 206.4°F |
| 5,000 feet | 202.75°F |
| 8,000 feet | 197.5°F |
If your readings are off at either test point, it is time to reset. If they match, no reset is needed.
Step 2: How to reset an infrared thermometer
Start by looking for a reset button. If your thermometer has one, follow the manual’s instructions for using it. If it has no reset button, the battery method below is usually the only home reset available; beyond that, contact the manufacturer for help.
- Remove the batteries for a short interval, no more than a few minutes.
- Reinstall the batteries and switch the thermometer on.
- Recheck accuracy using the ice or boiling point method.
- If it is still off, follow your manual’s calibration steps or contact the manufacturer or a calibration service.
When to check and reset
- When you first get a new thermometer.
- Regularly, for example once a month (weekly if you rely on it heavily).
- After it has been dropped.
- After changing the batteries.
- Whenever readings seem wrong or an error appears.
Keeping a simple log of when you checked and calibrated your thermometer makes it easier to spot problems over time.
FAQ
How do I switch an infrared thermometer to Fahrenheit?
The exact buttons vary by model, so check your manual. On many digital thermometers the process looks like this:
- Turn the thermometer off and wait until the display is completely blank.
- Wait about 10 seconds.
- Press and hold the mode or unit button until C or F appears.
- Use the same button to switch between the two and choose F.
- Turn the thermometer off, wait 10 seconds, then turn it back on. It should now read in Fahrenheit.
Many handheld models also have a dedicated °C/°F button or switch, sometimes inside the battery compartment. For background on the two scales, see Fahrenheit vs Celsius.
Why is my infrared thermometer not working?
There are three common problems, each with a different fix:
- It gives wrong readings: check accuracy, then reset using the steps above.
- It shows an error: an “Er” message usually means a reset or calibration is needed. Try the battery reset; if the error remains, contact the manufacturer.
- It won’t turn on: replace the batteries. If it still won’t power up, contact the manufacturer for repair or replacement.
How do I reset a thermometer used for fever checks?
The same battery reset applies to most digital medical thermometers, but don’t test a medical thermometer in boiling water. Follow the manufacturer’s instructions for checking and resetting it, and see how to take a temperature for correct technique.
Final thoughts
Most infrared thermometer “faults” are fixed by fresh batteries or a simple battery reset. Test against ice water or boiling water before and after, and if the readings still drift, the manufacturer is your best next step.
