What is a common consequence of incomplete combustion in a boiler?

Incomplete combustion in a boiler primarily leads to reduced fuel efficiency. This occurs when the fuel is not burned completely, resulting in unburned hydrocarbons and particulates. These leftover components indicate that not all the available energy from the fuel is being used to produce heat. As a result, the boiler must consume more fuel to achieve the desired output, ultimately decreasing overall efficiency.

Additionally, this situation can have cascading effects: higher fuel consumption directly contributes to increased operational costs. However, the question specifically asks about a common consequence, making reduced fuel efficiency the primary focus. Incomplete combustion does not yield lower emissions; in fact, it often leads to higher emissions of pollutants. Improved performance is also unlikely, as inefficiencies in combustion typically result in poorer functionality of the boiler system.