Why won’t my Samsung oven heat up as usual? The door may have been left open too long, enabling the oven’s automatic shut-off feature. Make sure the oven door is closed completely after opening it. Learn more reasons for a Samsung oven not heating properly to quickly solve the problem. 1. Oven not getting power. 2. Oven is still in Demo mode. 3. Opening oven door too much. 4. Need to recalibrate oven thermostat. 5. Oven bake element is defective. 6. Gas igniter has failed.