Diagnosis
The heating element is struggling, almost always due to a poor power connection from a damaged cord or plug.
How to Fix It
Inspect the entire cord, especially where it connects to the styler and at the wall plug. Look for kinks, fraying, or any exposed wire. Try a different, known-good wall outlet on a different circuit. Ensure you're plugging it directly into the wall, not a power strip or extension cord that can limit current.
If That Didn't Work
If the cord is intact and the outlet is good, the internal heating element is degrading. This is a gradual failure. The performance will continue to decline until it fails to reach temperature entirely. The element is not user-replaceable.
Heads Up
Using a voltage converter or transformer with this styler (for example, when traveling) will dramatically increase heat-up time and can permanently damage the element. It's designed for the voltage of the country it was purchased in.