What issue may arise when only four out of five ribbon burners are firing simultaneously?

When examining the situation where only four out of five ribbon burners are firing simultaneously, the alignment of the burners plays a crucial role in ensuring proper combustion and airflow across the entire system. If the burners are not aligned properly, it can result in uneven distribution of the flame, causing some burners to fail to ignite while others function correctly. Proper alignment ensures that each burner receives an equal amount of fuel and air mixture for efficient operation.

In contrast, issues such as an insufficient gas supply, insufficient air supply, or a defective main gas valve would likely affect all burners rather than selectively causing only one burner to fail to ignite. Therefore, the most plausible reason for this specific scenario involves the alignment issue of the burners themselves. Proper installation and adjustment are critical to maintain the effectiveness and reliability of the heating system as a whole.