What causes a dimmer switch to stop dimming?

A residential wall dimmer switch typically stops dimming properly due to several common electrical and hardware failures. The most frequent cause is bulb incompatibility, such as using non-dimmable LED bulbs or mixing bulb types that fall outside the dimmer's minimum and maximum wattage load thresholds. Other causes include internal solid-state triac component degradation, loose wire terminal connections causing voltage drops, or internal thermal overload from being installed in a multi-gang box without fin removal. You can troubleshoot dimmer issues easily by testing compatible bulbs. You can verify that your corrective action is successful when installing dimmable LED-rated bulbs, tightening loose wire connections, or replacing a failed dimmer restores smooth, graduated brightness adjustment.