All fired boilers that I have worked with have oxygen analyzers on their flue gas. Combining the oxygen concentration of the flue gas with the front-end air-to-fuel ratio can be very useful for quick troubleshooting. If you need a refresher on air-to-fuel ratio. The general concept is to calculate the expected concentration of oxygen in the flue gas from the air-to-fuel ratio and to compare it to the analyzer value. As I have spent more time in engineering and operations, I have seen more and more value in SIMPLE engineering checks. Here’s an example:
Research how your competition works especially their best practices and operating systems