Which one of the following is NOT a cause of insufficient low gas input?

Insufficient low gas input in a heating system can stem from various issues, but a faulty heat exchanger is not directly responsible for the low gas input. The heat exchanger's primary role is to transfer heat from the combustion gases to the air or water used in the heating system, rather than regulate the volume or pressure of gas being delivered to the burner.

In contrast, components like a dirty air filter, improperly adjusted gas valve, or a blocked venting system can directly impact the efficiency and performance of gas delivery. A dirty air filter can restrict airflow, leading to incomplete combustion and insufficient gas input. An improperly adjusted gas valve can result in the gas flow being too low, while a blocked venting system can create backpressure that affects how gas is utilized in combustion.

Understanding these relationships is vital for diagnosing and addressing issues in gas and oil heating systems effectively.