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Check an unexpected CO₂ reading

Let the sensor settle and avoid breath affecting the sample.

testo 535 — app-connected

Applies to: App-era 535, device 0560 0535 01 / kit 0563 0535 01.

Before you start: Handle the probe gently. Avoid condensation and strong vibration; do not open the sensor.

Identify the probe

Callout 3 is the upper probe. The rear grille, callout 4, is the alarm speaker.

Front and rear views of the app-era testo 535; callout 3 identifies its upper probe and callout 4 its rear alarm speaker.
Instrument and probe identification. Testo manual, page 6 ↗ · Select image to enlarge.

Allow settling time

Allow about 30 seconds for warm-up and about 60 seconds for CO₂ adjustment to the surroundings. After a temperature change, allow a few minutes to acclimatize.

Avoid exhaled breath

Keep the probe away from your breathing zone while measuring. Record where and how the reading was taken.

If the issue continues: For persistent unexpected values, record the value, units, conditions and stabilization time, then ask QRM to assess the meter.

Still need help with your device?

Include the model, serial number, exact error and checks already completed.

Start a service request

Source and applicability

testo 535 - Digital CO2 meter (0560 0535 01): Instruction manual — §5.1, p. 6; §7.2, p. 16. 0970 9535 en 01 - 12.2022

Open the complete Testo operating manual ↗ · Find this model in the manual list

QRM wording summarizes the checks. Diagram excerpts © Testo SE & Co. KGaA. Follow the complete manual and warnings for your instrument. Source checked 7 September 2026.