HVAC Contractor Practice Exam

A faulty ignitor is a common reason for a furnace failing to ignite because this component is responsible for providing the initial spark needed to light the gas fuel in the furnace. If the ignitor is malfunctioning, whether it's due to wear and tear, electrical issues, or physical damage, the furnace will not receive the spark necessary for ignition. Without this ignition source, the combustion process can't begin, leading to a complete failure to ignite.

While factors like excessive airflow, overheating, and dirty filters can also affect furnace operation, they may not directly lead to an immediate failure to ignite. Excessive airflow is more likely to impact furnace efficiency or cause operation issues rather than prevent ignition altogether. Overheating is typically a result of prolonged operation under fault conditions rather than a direct cause of ignition failure. Similarly, dirty filters might cause airflow restrictions, leading to other operational issues but not necessarily preventing the ignitor from doing its job when it is functioning. Hence, the condition of the ignitor is crucial in the ignition sequence of a furnace.