The answer to 'when to replace faucet' is that you should generally replace your faucet every 10-15 years, or sooner if it is leaking, dripping, or not functioning properly. Faucets are exposed to a lot of daily use and wear over time, so it's important to replace them before they start causing water damage or wasting water.
Signs it may be time to replace your faucet include low water pressure, difficulty turning the handles, visible corrosion or mineral buildup, and persistent leaks even after repairs. Replacing a faucet is a relatively easy DIY project, but you may want to call a professional plumber if you're not comfortable doing it yourself or if you have an older or more complex faucet.