In a gun-type oil burner, the primary control stops the burner if the flame goes out or if the flue temperature becomes too ______.

• A. High
• B. Low
• C. Moderate
• D. Extreme

Answer: (A)

The primary control in a gun-type oil burner protects against two dangerous conditions: loss of flame and overheating. It constantly checks that the flame is present and that the flue gases aren’t getting too hot. If the flame goes out, fuel can continue to be sprayed, creating a potential explosion or buildup. If the flue temperature becomes too high, it indicates overheating or restricted venting, which can damage the boiler and pose a fire hazard. To prevent these risks, the control shuts the burner when the flue temperature is too high. That’s why the correct completion is "too high." A low, moderate, or extreme flue temperature doesn’t trigger this safety shutdown the same way; the high limit is the protective threshold.