Err

Various Digital Thermometer

Severity: Minor

What it means

Digital thermometer 'Err' on the display is a general error code that means the device couldn't complete a reading.
Apollo Pharmacy's published thermometer error guide describes it as: 'a general code for a system error, indicating an internal malfunction or a technical fault. It could mean the test was interrupted or that the environment is too hot or cold.'
Most often Err is caused by movement during measurement, the probe coming away from the body, or the ambient temperature being outside the device's specified operating range.
The fix is almost always to switch the thermometer off, reposition properly, and retake the reading.

Affected Models

Body thermometers (oral, ear, forehead) — all major brands
Smart thermometers that pair with an app
Surface and cooking thermometers (less common on these — they tend to show OL or specific codes instead)
Pharmacy thermometers — Apollo brand and similar consumer thermometers
Err is a generic catch-all — different brands sometimes use 'Er', 'Er1', 'Er2', 'E1', or specific numbered errors instead

Common Causes

Movement during measurement (especially common on ear and forehead thermometers)
Probe lost contact with the body before the reading completed
Ambient temperature outside the device's operating range (typically 10-40°C / 50-104°F)
Battery too low to sustain a reading without the voltage drooping
Internal sensor or board fault (rare; usually after years of use or physical damage)

How to Fix It

Switch the thermometer off and on.

Apollo Pharmacy's published guidance: 'Press the on/off button to switch off the thermometer. Check if it is correctly positioned, press the on/off button again to switch it on, and re-start the measurement.'
A clean off-on cycle clears any transient error state — the same way restarting a phone fixes most software hiccups.
Stay still during measurement.

Ear and forehead thermometers especially are sensitive to movement.
Hold the device steady against the target area for the full measurement time (usually 1-3 seconds for ear, immediate for forehead, longer for oral and armpit).
If the person is a young child who won't stay still, take 2-3 measurements and use the highest reading.
Check ambient temperature.

Most consumer thermometers are rated for ambient operation between 10°C and 40°C (50-104°F).
If you've just brought the thermometer in from a cold car or hot shed, let it sit indoors for 15-30 minutes before using.
Below or above its operating range, the thermometer correctly refuses to give a reading and shows Err.
Replace the battery.

Many digital thermometers show Err as a low-battery warning when the battery can't sustain the sensor circuit voltage.
Open the battery compartment and replace the button cell (CR2032 or LR41 for most thermometers).
If Err appeared right when the device was due for a battery anyway, this is the fix.
Clean the probe.

For oral and rectal thermometers, wipe with alcohol and dry.
For ear thermometers, replace the disposable probe cover (if your model uses one) or gently clean the lens.
For forehead infrared, wipe the lens with a soft cloth lightly moistened with alcohol; never use harsh detergent or rubbing.
A dirty probe causes inconsistent readings that the thermometer flags as Err.
Replace the thermometer.

If Err appears every time even with a fresh battery, clean probe, and stable target, the internal sensor or board has failed.
Digital thermometers are inexpensive enough that replacement is almost always more economical than repair.
Choose a replacement that documents its full error code list — Apollo, Philips Avent, and Braun all publish complete error tables in their manuals.

When to Call a Professional

Err is owner-fixable in almost every case — restart the thermometer and retake the reading with attention to positioning.
Replace the battery if Err persists across multiple attempts.
If Err appears every time even with a fresh battery and correct technique, the thermometer's internal sensor or board has failed and replacement is the right call.

Frequently Asked Questions

My ear thermometer shows Err every time on my toddler — is it the device or the kid?

Probably the technique, not the device.
Ear thermometers need the probe to be aimed deeply enough into the ear canal — and on small children, you need to pull the ear gently down and back (the opposite direction from adults — adults: up and back) to straighten the canal first.
Insert the probe firmly until it seats, hold the trigger, wait for the beep.
If the child moves before the beep, Err fires.
Practical tip: have the child lie on their side or sit on a parent's lap to minimise movement.
If Err still appears with proper technique, then check battery and probe cleanliness — but technique is usually the cause.