Quick answer: The testo 330 measures flue-gas quantities for combustion service. Confirm the exact sensor and instrument generation, zero as directed, record stable oxygen and carbon-monoxide readings and interpret them against the appliance specification—not a universal target.
What makes the testo 330 different
The current testo 330 family has several sensor configurations: O₂/CO, CO with H₂ compensation, and configurations with an additional NO sensor. A statement about the 40,000 ppm extended CO capability only applies where the specified sensor and active dilution are present. For related guidance, see Combustion Test: Setup and Reading Interpretation : What makes.
Prepare and carry out the measurement
- Verify that a qualified technician has confirmed the appliance operating safely and identified an approved sampling point.
- Inspect the flue-gas probe, sampling hose, condensate protection and sensor status; complete fresh-air zeroing exactly as specified in the corresponding manual.
- Select the actual fuel and operating mode, and record burner load, flue/combustion-air temperatures and other installed sensor channels.
- Sample at the specified point with proper probe placement, wait for stable O₂ and CO and save the values together with the operating condition.
Model-specific use and interpretation
Use the 5.5-inch touchscreen workflow on the current 330 generation; older 330 versions require their own manuals. Record the part number and which gas sensors are fitted before selecting a test sequence.
O₂ indicates residual oxygen, CO indicates incomplete-combustion product and flue temperature supports the calculated flue-loss estimate. A calculated combustion-efficiency percentage is not seasonal appliance efficiency. Sensor configuration and fuel choice change what can be displayed. For a broader explanation of combustion measurements and calculated efficiency, see flue gas analyzer readings.
When comparing O₂, CO and optionally NO at different firing points, label the load and any dilution or reference-oxygen correction.
Worked example (hypothetical)
Hypothetical record: at one stable burner condition O₂ is 5.2%, CO 18 ppm and flue temperature 150 °C. At another condition the values are 4.7%, 26 ppm and 165 °C. The changes are -0.5 percentage points O₂, +8 ppm CO and +15 °C; they cannot be judged safe or optimal without appliance criteria and comparable load conditions.
If the readings change unexpectedly
- Recheck probe location, blocked sampling hose, condensate trap, sensor zero and the fuel setting before concluding that combustion changed.
- If O₂ and CO drift together, review appliance operating state and combustion-air supply under an approved service protocol.
- If there is unsafe CO, spillage, incomplete combustion or any hazard indication, stop the measurement and follow the applicable emergency and professional service procedures.
Choose the correct CO/NO configuration
A current testo 330 sold as O₂ + CO is not functionally identical to a CO/H₂ or NO-equipped version. The extended CO range published for certain configurations should never be used to infer the range of an unverified device. Before a combustion investigation, check the type plate, sensor menu and manual, then document whether measured NO is available. A change in NO during tuning is not an adequate reason to ignore a dangerous CO result. For a structured way to document the appliance, fuel, analyzer configuration and measured results, see this boiler combustion test report.
Interpretation: An equipment record may include O₂ 5.0%, CO 20 ppm and “NO not fitted.” The missing NO is a hardware limitation, not a zero emission.
Limits and safety
Follow the exact instrument manual and the equipment manufacturer’s acceptance criteria. The example is not field evidence, a legal limit or a commissioning target. Work on energized electrical equipment, combustion systems, charged refrigerant circuits or hot surfaces requires qualified personnel and the site’s approved protective procedures. For a broader procedure covering combustion-analyzer setup, readings and efficiency limits, see this boiler efficiency testing guide.