Diagnosis
The heater’s built-in thermostat is likely getting fooled by its own heat output. If the heater is placed in a corner, on a shelf, or too close to a wall, the hot air bounces right back into the thermostat sensor, making it think the whole room is warm, so it shuts off prematurely.
How to Fix It
Relocation is key. 1) Unplug the heater. 2) Move it to the center of the room or at least several feet away from any walls, furniture, or curtains. 3) Place it on the floor, not on a table or shelf. Heat rises, so putting it low helps it sense the true room temperature better. 4) Plug it back in and set the thermostat dial to a medium setting. Let it run a full cycle. You should notice it stays on longer and heats more consistently.
If That Didn't Work
The thermostat dial itself, a simple mechanical component behind the control knob, can wear out or get dirty. You can try spraying a small amount of electronic contact cleaner (not WD-40) into the base of the knob while rotating it back and forth to clean the internal contacts. If that doesn’t help, the thermostat unit may need to be replaced.
Heads Up
Don’t use an external plug-in thermostat with this heater. It’s not designed for that kind of control and it can cause conflicting cycles that are hard on the internal components.