The answer to 'when to replace shut-off valve' is that you should replace a shut-off valve when it becomes difficult to operate or begins to leak. Over time, the internal components of a shut-off valve can wear out, leading to problems like leaks or the valve becoming stuck in the open or closed position.
It's generally recommended to replace a shut-off valve every 10-15 years, or sooner if you notice any issues with it. Signs that a shut-off valve needs replacement include difficulty turning the valve, dripping water even when the valve is closed, or the valve not completely shutting off the water flow. Replacing a worn-out shut-off valve can help prevent water damage and ensure you can reliably control the water supply to your home.