Which safety device is designed to detect flame rollout and open the circuit if flame is not contained?

Which safety device is designed to detect flame rollout and open the circuit if flame is not contained?

• A. Draft switch
• B. Rollout switch
• C. Flame sensor
• D. High-limit switch

Answer: (B)

Flame rollout happens when flame and combustion gases escape the burner enclosure and reach parts of the furnace cabinet. A rollout switch is specifically placed to sense that hazardous condition and will open the circuit if rollout is detected, which shuts off the gas supply or the control circuit to stop the burner. This immediate shutdown helps prevent a fire inside the furnace and limits exposure to combustion byproducts. A draft switch, by contrast, monitors the overall venting flow to ensure there’s enough draft to carry combustion products out of the house; it isn’t meant to detect flame reaching the cabinet. A flame sensor checks whether a flame is actually present to keep ignition under control, not to detect rollout. A high-limit switch tracks temperatures to prevent overheating, not to detect flame containment issues.

Flame rollout happens when flame and combustion gases escape the burner enclosure and reach parts of the furnace cabinet. A rollout switch is specifically placed to sense that hazardous condition and will open the circuit if rollout is detected, which shuts off the gas supply or the control circuit to stop the burner. This immediate shutdown helps prevent a fire inside the furnace and limits exposure to combustion byproducts.

A draft switch, by contrast, monitors the overall venting flow to ensure there’s enough draft to carry combustion products out of the house; it isn’t meant to detect flame reaching the cabinet. A flame sensor checks whether a flame is actually present to keep ignition under control, not to detect rollout. A high-limit switch tracks temperatures to prevent overheating, not to detect flame containment issues.