How much of the pilot flame should engulf the thermocouple?

How much of the pilot flame should engulf the thermocouple?

• A. 1/4 inch
• B. 1/2 inch
• C. 1 inch
• D. 2 inches

Answer: (B)

The thermocouple needs to be heated sufficiently by the pilot flame to generate the voltage that keeps the gas valve open. If only a small portion of the thermocouple tip is in the flame, the tip won’t heat enough and the system may fail to hold the valve open, causing the pilot to go out. If the flame engulfs too much of the tip, it isn’t necessary and can waste heat or cause excessive wear. Engulfing about half an inch of the thermocouple tip provides reliable heating, producing the needed millivolts while staying within a safe, efficient range. Therefore, around 1/2 inch of the pilot flame should envelop the thermocouple.

The thermocouple needs to be heated sufficiently by the pilot flame to generate the voltage that keeps the gas valve open. If only a small portion of the thermocouple tip is in the flame, the tip won’t heat enough and the system may fail to hold the valve open, causing the pilot to go out. If the flame engulfs too much of the tip, it isn’t necessary and can waste heat or cause excessive wear.

Engulfing about half an inch of the thermocouple tip provides reliable heating, producing the needed millivolts while staying within a safe, efficient range. Therefore, around 1/2 inch of the pilot flame should envelop the thermocouple.