What action should be taken if leakage is indicated by a test device as per NFPA 54 C.4?

The correct action to take if leakage is indicated by a test device, as per NFPA 54 C.4, is to examine all appliances for leaks. This approach ensures a thorough investigation of the entire system. When a leak is detected, it may not necessarily be limited to one specific appliance; other appliances or components within the gas system could also be affected. By examining all appliances, you can identify any additional sources of leakage, ensuring that the entire system is safe and compliant.

This comprehensive check is important not only for safety reasons but also for system integrity, as any undetected leaks could lead to potentially dangerous situations over time. While the other options suggest actions related to repairs or adjustments, they do not address the immediate need to fully assess the state of the entire system following a leak indication.