A flame failure device is a safety mechanism used in gas appliances, such as boilers and water heaters. Its primary function is to detect if the flame goes out unexpectedly. If this occurs, the device automatically shuts off the gas supply to prevent the risk of gas leaks and potential explosions. These devices typically use a thermocouple or thermopile to monitor the flame's presence. When the flame is detected, the device allows gas to flow; if the flame extinguishes, the device quickly cuts off the gas. This ensures safe operation and protects users from hazardous situations.