DIAGNOSIS Dust accumulation on the heating fins is burning off, causing the smell and reducing efficiency.
FIX Unplug and cool the heater completely. Use a vacuum cleaner with a soft brush attachment. Gently vacuum the fins from top to bottom. For stubborn dust, use a can of compressed air (held upright) to blow dust out from the back. Wipe the exterior with a damp cloth only.
IF THAT DIDN'T WORK If a burning plastic smell persists, inspect the power cord and plug for damage. Do not operate if the cord is damaged.
HEADS UP Never use water, cleaning fluids, or insert objects between the fins. Do not tip the heater on its side while cleaning.