Diagnosis
The oscillation feature is driven by a small electric motor and gear assembly. It can stop if the mechanism is physically obstructed, the gear is stripped, or the motor fails.
How to Fix It
First, unplug the heater. Get down and look closely at the base. Manually try to turn the heater side-to-side on its base. It should move smoothly. If it's stuck, check for carpet fibers, a stray cord, or any debris jammed in the seam between the rotating top and the stationary base. Clear anything you find. Plug it back in, press the oscillation button, and gently assist the start of the turn with your hand. Sometimes it just needs a nudge to overcome initial friction.
If That Didn't Work
If the mechanism moves freely by hand but the motor doesn't engage when you press the button (you might hear a faint hum or click but no movement), the internal plastic gear or motor is likely broken. This is a very common point of failure on many oscillating heaters and fans. Repair requires disassembling the base and sourcing a replacement gear or motor, which isn't practical for most people.
Heads Up
Forcing the oscillation by hand while the motor is trying to run can strip the plastic gear. If you're helping it start, do it gently and only for a half-second to get it moving. If it doesn't start on its own after that, the motor isn't strong enough and the part is probably worn out.