What happens when a burner is shut down?

• A. Fuel pressure goes up
• B. Fuel pressure goes down
• C. O2 readings become unstable
• D. Flow of fuel stops immediately

Answer: (A)

When the burner is shut down, the fuel valve closes and stops fuel entering the burner, but the fuel pump continues to push. With the outlet blocked, the pressure in the fuel line ahead of the closed valve increases because the pump is still supplying fluid but there’s no place for it to go. Downstream pressure drops toward zero since fuel can no longer reach the burner. Oxygen readings aren’t directly tied to this shutdown action, and while a brief moment of residual flow can occur due to line volume, the overall effect you’ll observe is a rise in fuel pressure upstream of the closed valve.