Quick answer: The testo 320 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 320 different
The current testo 320 (0633 3200 01) has a 5.5-inch touchscreen and integrated O₂/CO sensors, with an advertised CO range to 5,000 ppm. The older testo 320 family also exists: do not apply the touchscreen instructions to a keypad-era unit. For a related analyzer model, see testo 300 combustion analyzer setup.
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
Confirm the product code on the label, perform the manual-specified zero, use the guided measurement program and verify the connected flue probe. The Smart App can provide a second screen and reporting for compatible current hardware.
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 these measurements, see flue gas analyzer readings explained.
Use the logged O₂ (% vol), CO (ppm) and flue temperature together; the calculated flue-loss/efficiency number is not whole-season boiler performance.
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.
Identify new and legacy testo 320 units
The product code 0633 3200 01 identifies the new 5.5-inch touchscreen version described by Testo. It supports testo Smart App integration and measurement/reporting workflows not necessarily found on old keypad-era devices. Before a technician follows screen instructions, compare the model sticker and the manual illustrations. Do not report draft, temperature or ambient CO as measured unless the corresponding probe or sensor and configuration are available.
Interpretation: If a report displays only O₂, CO and one temperature, the technician should not invent omitted pressure or ambient readings to fill a checklist. For reporting requirements, see boiler combustion test report guide.
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.