What is generally not a result of scorching inside a burner access door?

Scorching inside a burner access door typically indicates a problem occurring within the combustion process of the appliance. This scorching is often due to excessive heat, which can result from several issues related to combustion efficiency, such as improper fuel-air mixtures or insufficient ventilation.

Regarding the options, lack of combustion air is not generally a result of scorching seen inside a burner access door. Instead, a deficiency in combustion air typically leads to incomplete combustion, producing soot rather than scorching. Scorching suggests that combustion is occurring excessively or improperly, often due to an overabundance of fuel relative to air, leading to elevated temperatures at the burner.

In contrast, chimney obstructions can restrict the flue gases from exiting efficiently, closing off the exhaust path and causing heat accumulation, leading to scorching. A faulty high-limit switch may cause the appliance to exceed safe temperature limits, contributing to scorching as well. Under-firing, which refers to insufficient fuel being delivered for combustion, can result in incomplete burning but may not directly lead to scorching.

Therefore, the absence of combustion air does not create the high temperatures that lead to scorching symptoms, making this choice the most appropriate in identifying what is not an outcome of scorching inside a burner access door.