Which of these is a sign of a potential gas leak?

A yellow or orange flame in appliances is indeed a sign of a potential gas leak or incomplete combustion. In a properly functioning gas appliance, the flame should burn blue, indicating that the gas is burning completely and efficiently. When the flame appears yellow or orange, it suggests that not all the gas is being burned, which can occur due to a gas leak, incorrect air-to-gas mixture, or other malfunctions. This change in color can also indicate the presence of carbon monoxide, which is a dangerous byproduct of incomplete combustion.

While the other options may suggest issues—such as an increased water bill possibly indicating a plumbing issue or excessive noise from the gas line pointing to a problem—only the color of the flame directly relates to the combustion of gas and serves as a visual cue that there may be an unsafe situation that needs to be addressed immediately. Identifying such a flame color is critical for safety in any environment where gas appliances are used.