There are several different types of dimmer switches available for home use, including push-buttons, sliding switches, rotating dials and automatic dimmers. Dimmers work by restricting the flow of current to the switch, which in turn dims the lights. If a light stops working when you turn on the switch, it could mean that the light is burnt out, the breaker is off or tripped, or the switch itself is faulty. One way to check the switch is with a continuity tester.
Cut the power to the switch by turning off the appropriate breaker or pulling the fuse. Turn the light switch on to double-check that the power is off.
Remove the rotating dial if equipped and the switch cover plate by turning the top and bottom screws counterclockwise.
Touch one probe of the tester to a black wire terminal and one prone to a white wire terminal. If the switch is good, the tester will light up or buzz.
Turn the switch off. The tester should not light up or buzz.
Replace the cover plate and the rotating dial.