Why might the relief valve leak after closing the customer's shut-off valve?

The leaking of the relief valve after closing the customer's shut-off valve can indicate that there is a backflow condition or a failure in one of the system components. When considering that CV #1 leaks, it suggests that there is a fault that allows water to escape, forcing the relief valve to open. This scenario illustrates a failure of the check valve, which is intended to prevent backflow and protect the water supply from contamination.

When a check valve is functioning correctly, it should prevent reverse flow and maintain appropriate pressure within the system. If it leaks, it results in a pressure imbalance, leading the relief valve to release water to mitigate the risk of overpressure or backflow. Therefore, identifying a leak at CV #1 is essential in troubleshooting the issue, as it directly affects the operation of the relief valve and the system overall.

Understanding that this condition points to a mechanical failure helps highlight the need for regular inspections and maintenance to ensure all components, including the check valve, are functioning correctly to prevent leaks and maintain system integrity.