Which of the following can indicate a problem with combustion in a boiler?

High emissions and soot buildup are clear indicators of combustion problems in a boiler. These issues typically arise when the fuel is not burning completely, which can be caused by several factors, such as improper air-to-fuel ratios, insufficient oxygen supply, or malfunctioning burners. When combustion is inefficient, it leads to an increase in unburned carbon and other pollutants, resulting in higher emissions and the physical accumulation of soot within the boiler. This not only diminishes efficiency but can also lead to more serious operational risks and increased maintenance needs if not addressed promptly.

In contrast, stable pressure readings, clear water discharge, and low fuel consumption do not indicate combustion issues. Stable pressure readings suggest that the boiler is operating efficiently. Clear water discharge may indicate proper boiler function and appropriate blowdown practices, while low fuel consumption, under the right conditions, may suggest efficient operation rather than problems with combustion.