In burner safety switches, the bi-metal element expands to do what when heated by the hot gas?

• A. Open the hot contacts
• B. Cool the safety switch
• C. Expand and close the hot contacts
• D. Shrink and disconnect the circuit

Answer: (C)

A bi-metal element uses two metals with different expansion rates, so when heated by the burner’s hot gas it actually expands and causes the mechanism to move. In burner safety switches this expansion makes the contacts come together, closing the hot contacts and completing the circuit to energize the burner valve or ignition system. This design ensures the burner stays lit as long as the flame remains hot; if the flame goes out and the element cools, it contracts and the contacts open, cutting off the gas supply. So the expansion leading to closing the hot contacts is the behavior that matches how the switch regulates burner operation.