While trying to light off a burner on a semi-automated boiler, you note that the fuel oil solenoid valve at the burner will not stay open. Which of the following conditions could cause this problem?

Correct Answer: Option B — The forced draft air supply has failed.

Burner safety interlocks require adequate forced draft air pressure to prove combustion air flow before energizing the fuel oil solenoid valve. A failure in the forced draft air supply trips the airflow switch, preventing the burner safety circuit from opening the fuel valve.