Weighted blankets typically cannot be machine washed in a home washer due to their heavy design. If you do wash your weighted blanket at home, you risk damaging your machine washer, not just the blanket itself.
Taking it to a laundromat can let you use a machine for heavier loads. Alternatively, a dry cleaner can clean it down to the fibers by using specialty chemicals, avoiding the damage that water can cause to a weighted blanket's materials.