DIAGNOSIS Overload protection. The space heater's startup surge (inrush current) exceeds the unit's 2000W surge capacity or its 1000W continuous rating. The BMS is cutting power to protect the inverter.
FIX Do not use high-surge resistive loads like space heaters or hair dryers. They are incompatible. Use the Jackery for electronics, tools, or appliances with a motor rated under 1000W. Check the heater's label—it likely draws 1500W.
IF THAT DIDN'T WORK If a lower-wattage device also causes a triple-beep shutdown, test the unit with a known-good, low-draw device like a phone charger. If it fails, the inverter MOSFETs or current sensors are faulty.
HEADS UP The 1000W rating is for continuous sine wave output. Resistive heating loads draw their full rating continuously. You have no headroom. Using it this way will trip protection or damage the unit.