Red Seal Gasfitter — Class B Practice Exam

What does a yellow flame in a gas appliance indicate?

1. Proper combustion

2. Incomplete combustion

3. Excessive gas flow

4. Normal operation

The correct answer is: Incomplete combustion

A yellow flame in a gas appliance is an indication of incomplete combustion. This occurs when there is not enough air mixed with the gas during the burning process, leading to a cooler flame that produces yellow or orange tips. The yellow color typically suggests that the appliance is generating carbon particles, which can be seen as soot or a yellow, flickering flame rather than a clean blue flame. Incomplete combustion not only affects the efficiency of the appliance, causing it to waste fuel, but it can also lead to the production of carbon monoxide, a dangerous and potentially deadly gas. Proper combustion is characterized by a steady blue flame, which indicates that enough air is present for complete burning of the gas. Therefore, recognizing a yellow flame is crucial for ensuring both safety and efficiency in the operation of gas appliances.