I love dimmer switches; I use them to control almost every light in my house. Installing a dimmer switch is a common enough DIY project, but like any other DIY project, I often find them installed improperly. The most common problem I find is when dimmer switches are connected to a ceiling fan.
Standard dimmer switches should never be used on ceiling fans because they could damage the fan motor or they could overheat and start a fire. To know whether a dimmer switch is intended for use with a fan, all you usually have to do is remove the switch cover; there is typically fine print right on the front of the switch saying whether or not it can be used with a ceiling fan.
The photo below left comes from a fan speed controller – this is what needs to be used on a ceiling fan. The photo below right comes from a standard dimmer switch, and this should not be used on a ceiling fan.
When I find a dimmer switch that is designed for incandescent fixtures connected to a ceiling fan, I always recommend repair. A safe repair can be as simple as replacing the dimmer switch with a standard toggle switch, but you also lose the ability to dim the light.
If the wiring for a ceiling fan is already in place in your home (ie – you have separate wires for the fan control and the light control), it should be fairly easy for a qualified person to wire up separate controls for the fan and the light, which will include the ability to dim the light.
If the ceiling fan was a retro install, there probably won't be proper wiring in the wall for separate fan and light controls; not to worry though. You can actually purchase a device that will do this – it consists of a wireless remote and a receiver that gets wired directly in to the fan. These devices work very well, and as far as I know, they can be used with any ceiling fan.