When performing a combustion test, one of the most important concepts to understand is stability of the combustion process. If the combustion process is not stable, it is not safe. Once a flame is established, the burner should quickly reach study state operation and not be affected by factors external to it.
While the combustion process is not adjustable, it is dynamic. Many factors of the installation and operation can and do affect the combustion process. Without verifying that the combustion process is safe, stable and within the manufacturer or industry standard guidelines you are putting yourself and your customers at risk. Simply, what you cannot see can hurt you, so the only way to know is to measure.
When looking at the recording above done with a Testo 330, it is easy to see that the O2 and the stack temperature are unstable. These measurements we made on a commercial boiler that is being subjected to depressurization of the combustion air zone (CAZ). As can be seen, when the O2 dropped to its lowest point, the CO made a rapid increase as incomplete combustion occurred. What is most interesting is the fact that the changes in O2 do not cause a change in the CO until the O2 level drops to about 7% for this burner. If you were just observing the CO and not watching the O2, you would miss a telltale sign of a serious combustion problem. This is easily seen with the 330 with easy heat software in the online mode, but it can also be observed on the 327 or 325M if the technician carefully watches the O2 level and monitor the CO air-free. At no time should a residential or commercial burner used for heating produce a stack level CO reading above 400 ppm air free (COAF)
Above is a boiler operating normally. A stable O2, stack temperature and a CO level close to 0 ppm show ideal combustion.
The moral of the story….. If the combustion process is not stable, it is not safe. It is the responsibility of the technician to determine what is affecting the process and eliminate the cause. Anything else is providing substandard service. The testo 330 and the 327 do a lot more than measure CO, make sure you get the most out of your investment.