What is a primary cause of burner "flashback"?

A primary cause of burner "flashback" is low manifold pressure. This phenomenon occurs when there is not enough pressure in the gas supply to maintain a stable flame at the burner outlets. When the manifold pressure drops too low, the gas does not adequately mix with air to form a proper combustion mixture, leading to unstable combustion conditions. This can cause the flame to be drawn back into the burner assembly rather than remaining stable at the burner ports, resulting in flashback, which is characterized by the flame moving along the gas supply line or back into the burner itself.

Understanding this concept is crucial for safe and effective furnace operation. It highlights the importance of monitoring and maintaining proper gas supply pressures to ensure efficient performance and prevent dangerous scenarios that can arise from flame instability.