Thermometer Error Codes: LO, HI, ERR, E1 and E2 Explained

Before Interpreting Any Thermometer Error Code

Write down these details first:

• The thermometer model and product number.
• The code exactly as shown on the screen.
• Whether it appeared at startup or during measurement.
• Whether the device was in Body or Surface mode, when applicable.
• The measurement site, distance or probe placement.
• Battery condition and room temperature.

The same code can mean different things on different models. These details help prevent random troubleshooting and, importantly, prevent a device message from being mistaken for a medical diagnosis.

Common Thermometer Error Codes

Why Does LO Appear When the Thermometer Starts?

On some contact thermometers, LO can appear before the probe is placed because the sensor is detecting a temperature below the device’s body-temperature measuring range. If the message disappears and a completed reading appears after correct placement and the completion beep, this may be normal behavior for that model.

It becomes a troubleshooting issue when LO continues during a properly performed measurement or appears instead of a result every time. Then check probe position, skin contact, whether you waited for the completion signal, and battery condition.

LO on a Non-Contact Forehead Thermometer

LO can appear when the device is in Body mode but is aimed too far away, the measuring distance is incorrect, the forehead is unusually cold after coming indoors, or the sensor is not aimed at the intended area. Do not simply move the device closer at random; use the distance specified in the manual and any positioning guide built into the model.

Also check that you did not use Surface mode and then interpret the result as body temperature. Body and object/surface modes can use different ranges and calibration logic.

When Could a Low Temperature Reading Be Real?

A completed low numerical reading is different from seeing the LO code. If a low number repeats with correct technique and the person has symptoms such as confusion, marked drowsiness, severe shivering or significant cold exposure, seek medical assessment. Do not use the LO message alone to conclude that a person has hypothermia.

Why Does HI Appear?

• The detected value is above the model’s measuring range.
• Body mode was used on a hot surface.
• The thermometer was stored near a heat source or used outside its specified operating environment.
• The sensor is dirty or has been exposed to a sudden temperature change.
• A genuinely high body-temperature reading may need confirmation and medical interpretation depending on symptoms and age.

Move the thermometer away from external heat, allow it to acclimatize to the room, clean the sensor only as instructed by the manufacturer, and repeat the measurement correctly. If the device produces a completed high numerical reading and the person has concerning symptoms, focus on the person’s condition rather than endlessly testing the device.

How to Fix ERR Step by Step

1. Turn the device off: wait briefly, then restart it.
2. Check the mode: use Body for body temperature and Surface/Object mode only for supported non-body measurements.
3. Repeat the correct technique: keep a contact probe in place until the completion signal, or use the correct distance and angle for a non-contact model.
4. Clean the sensor: only with a method permitted by the manufacturer, then let it dry completely.
5. Check the battery: replace a low battery with the specified type.
6. Check the environment: operate the thermometer within its specified temperature and humidity range.
7. Record the error: if it repeats, photograph the screen and note exactly when it occurs.

E1, E2 and E3: Why There Is No Universal Meaning

E1, E2, E3 and similar codes are not universal standards. E1 on one thermometer can mean something completely different from E1 on another. Searching the code without the model number can therefore lead to incorrect instructions.

Use the Troubleshooting, Error Messages or equivalent section of the exact model manual. For Medisana devices, you can search the official Medisana document library using the product or model number.

Battery Symbol and a Dim Display

A weak battery may cause a dim display, shutdowns or failure to begin a measurement. Use the battery type specified in the manual; a battery that physically fits is not necessarily electrically correct. Insert it with the correct polarity.

If a battery has leaked, avoid direct contact with the leaked material and stop using the thermometer until it has been inspected or safely replaced.

The Thermometer Works, but the Numbers Keep Changing

Changing numerical readings are not necessarily an error-code problem. Variations can result from changing the measurement site, time, distance, technique or device. Repeat measurements using the same site and method, and follow the user manual rather than repeatedly restarting the thermometer.

For a correct contact-temperature technique, see our guide on how to measure temperature under the armpit.

When Does the Thermometer Need Technical Support?

• ERR continues after a fresh battery and correct technique.
• The lens, probe or display is physically damaged.
• Liquid has entered the battery compartment.
• A code appears that is not documented in the user manual.
• The device repeatedly shuts down or becomes abnormally hot.

Do not open the device if doing so would violate its warranty or safety instructions. When contacting support, provide the model number, a photo of the code, battery type and the conditions in which the error appears.

When the Person Matters More Than the Device

If the person has breathing difficulty, altered consciousness, a seizure, a concerning rash, neck stiffness or obvious deterioration, seek medical help and do not let thermometer troubleshooting delay care. Use another suitable thermometer if one is available, but do not postpone assessment while trying to clear an error code.

Frequently Asked Questions

What does LO mean on a digital thermometer?

It often means the detected value is below that model’s measuring range or that body temperature was not captured correctly. On some contact thermometers it can appear normally before the probe reaches body temperature. The exact meaning must be confirmed in the model manual.

Does LO mean my body temperature is dangerously low?

Not by itself. LO is a device message, not a diagnosis. A completed low numerical reading taken correctly, especially with symptoms, should be interpreted separately and may need medical assessment.

What does HI mean on a thermometer?

HI commonly indicates that the detected value is above the supported range for the current mode, but external heat, incorrect mode or operating conditions can also trigger it. Check the manual for the exact model.

How do I clear ERR?

Restart the thermometer, verify the measurement mode and technique, check and replace the battery if needed, confirm the operating environment and inspect the sensor. If ERR persists despite correct use, consult the model manual or technical support.

Are E1 and E2 the same on every thermometer?

No. E1, E2 and similar codes are model-specific. Always interpret them using the exact device manual.