Which of the following can indicate that the gas pressure is too low?

The indication that the gas pressure is too low is represented by the main burner failing to light. This is because a proper gas supply pressure is essential for the burner to ignite effectively. When the pressure is insufficient, the gas does not reach the burner in the necessary quantity, which can lead to ignition failure because the fuel-air mixture is not optimal for combustion.

In a properly functioning system, a bright blue flame signifies good combustion with the right pressure and airflow. A strong smell of gas typically indicates a leak or an overpressure situation, rather than low pressure. Similarly, noisy operations might indicate improper functioning due to several factors, including but not limited to airflow issues or equipment malfunctions, rather than specifically pointing to low gas pressure. Therefore, the primary indicator of low gas pressure is when the main burner fails to ignite, highlighting the criticality of adequate gas supply for burner operation.