What type of flame indicates incomplete combustion in gas appliances?

Incomplete combustion in gas appliances is indicated by a yellow flame. A yellow flame typically results from an inadequate supply of oxygen, which prevents the gas from burning completely. This incomplete combustion produces a mixture of carbon, which is visible as soot, and unburned hydrocarbons, which can manifest as a yellowish appearance in the flame.

In contrast, a blue flame is indicative of complete combustion, where there is sufficient oxygen for the gas to burn efficiently, leading to a clean and efficient flame without excessive soot or harmful byproducts. Green flames are generally associated with the presence of copper vapor or certain additives in gas combustion, while purple flames are less common and can indicate various chemical reactions or specific additives, but they do not typically relate to the efficiency of gas combustion in residential or commercial applications.

Understanding the color of the flame helps in diagnosing issues with gas appliances, ensuring they are operating safely and efficiently.