Diagnosis
The heater draws up to 1500 watts (12.5 amps). Most lightweight household extension cords can't handle that sustained load, causing them to overheat and trip or become a fire hazard.
How to Fix It
The only safe fix is to plug the heater directly into a wall outlet. If you absolutely must use an extension cord, it MUST be a heavy-duty cord rated for at least 1875 watts (15 amps), be as short as possible (like 10 feet max), and have a 14-gauge wire thickness or lower (like 12-gauge). Never coil or cover the cord while in use.
If That Didn't Work
If it's still tripping with a proper heavy-duty cord, the problem might be your wall circuit. The heater should be on a dedicated circuit if possible. If it's sharing a circuit with other high-draw appliances (like a microwave or vacuum), it can trip the household breaker.
Heads Up
This is serious. Using an undersized extension cord is one of the top causes of space heater fires. explicitly warns against it for a reason. If the plug or cord feels hot to the touch, you're using the wrong cord.