Diagnosis
Dust buildup on the ceramic heating element or the aluminum fins is burning off, causing the smell and reducing efficiency.
How to Fix It
Unplug and let cool. Remove the rear grille. It is held by clips. Use a vacuum cleaner hose with a brush attachment to gently remove loose dust from the fins and element. For stuck-on dust, use a soft brush (like a paintbrush) to dislodge it, then vacuum.
If That Didn't Work
For persistent burnt smell, the dust may be deep in the element core. You may need to use compressed air in short bursts from the front, blowing backward out the rear, while vacuuming simultaneously.
Heads Up
Do not use liquids or damp cloths on the internal components. Do not bend the aluminum fins. They are fragile.