The answer to 'when to replace dimmer switch' is that you should replace a dimmer switch when it starts to malfunction or show signs of wear and tear. Dimmer switches typically last 5-10 years with normal use, but factors like frequency of use, electrical load, and environmental conditions can affect their lifespan. Signs it's time to replace a dimmer include flickering lights, the switch feeling loose, buzzing or humming noises, or the switch no longer providing smooth dimming control.
Replacing a dimmer switch is a relatively straightforward DIY task, but it's important to turn off power to the circuit at the circuit breaker first and follow proper safety precautions. If you're not comfortable working with electricity, it's best to hire a licensed electrician to handle the replacement.