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Service · Repair · CalibrationTesto instrument support, Canada
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Troubleshooting & walkthroughs

Illustrated checks for common Testo device symptoms, with a clear next step if the issue continues.

Find your next check

Choose the exact model and what you are seeing.

Start with the instrument safely out of service. Let hot probes cool. Refrigeration connections must be safely isolated and depressurized by a qualified technician before handling. Stop if there is damage, liquid inside the housing, a persistent fault, or a safety concern. These guides cover the instrument; they do not direct burner adjustment or refrigerant charging.

Browse illustrated walkthroughs

8 illustrated guides

Next-Gen testo 300 condensate outlet with its tethered sealing plug open; the manual highlights the outlet.
Next-Gen testo 300

Empty the condensate trap

Water visible in the trap? Check the outlet and seal.

View 3-step guide
Hands holding the modular flue gas probe for a Next-Gen testo 300 at its transparent particle-filter chamber.
Next-Gen testo 300

Inspect the modular-probe filter

Check the external probe filter when flow is weak.

View 3-step guide
Hand holding the testo 310 II with its condensate outlet facing up and the orange sealing plug lifted.
testo 310 II

Drain the 310 II condensate trap

Empty collected water and reseal the outlet.

View 3-step guide
Transparent filter chamber on the testo 310 II flue gas probe, with the manual arrow showing an anticlockwise opening turn.
testo 310 II

Check the 310 II probe filter

Inspect and replace the specified particle filter.

View 3-step guide
Rear battery cover of a testo 550s/557s manifold, with the suspension hook folded out and a hand releasing the cover clip.
testo 550s / testo 557s

Check the manifold batteries

Start here for a blank display or low battery.

View 3-step guide
testo 550s/557s Bluetooth menu showing Bluetooth ON and the Completed button selected.
testo 550s / testo 557s

Reconnect Bluetooth probes or the app

Check the manifold’s Bluetooth setting.

View 3-step guide
Front and rear views of the app-era testo 535; callout 3 identifies its upper probe and callout 4 its rear alarm speaker.
testo 535 — app-connected

Check an unexpected CO₂ reading

Let the sensor settle and avoid breath affecting the sample.

View 3-step guide
testo 435 overview with callout 5 below the instrument marking the probe sockets at its base.
testo 435 family

Check a plug-in probe connection

Connect the correct probe before switching on.

View 3-step guide
testo 320

Check sensor-care basics

Review model, sensor configuration, zeroing, filters and condensate before relying on a combustion reading.

Open the sensor-care guide

Still need help with your device?

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

Start a service request