Switches and dimmers operate lighting fixtures. Dimmers can reduce the energy and control the lighting levels, usually one switch/dimmer to one fixture or one set of fixtures. Dimmers come in many levels of dimming capacity The most commonly used are 600 watt and 1000 watt. You can determine your need by counting the total wattage of each lamp used on the dimmer. The closer you get to the maximum wattage of the dimmer, the warmer it will become. This is normal. The dimmer depresses the electrical wave which creates heat and the heat needs to dissipate.
To reduce the heating effect, you can increase your dimmer to the next wattage size. Switches/dimmers can stop operating from age, usage or shorting out. Switches/dimmers come in various shapes and styles. Switches come in toggle (standard style) to decora (rectangular/rocker style). Dimmers come with the same options with ranges from rotary (knob style), toggle, decora and touch (smooth faced). There are three-way switches/dimmers that can operate the fixture from multiple locations. Three-way dimmers can either be dimmed on one end of the switches or on both ends. Contact a licensed electrical contractor for these replacements.