Boiling water without burning it

Take bones. Add a halved onion, two carrots in large chunks, a couple stalks of celery in large chunks, two to three whole cloves of garlic, about 20 peppercorns, a couple of whole cloves, and some thyme, if desired. Put them all in a big crockpot, and cover with water. Let cook on low for 6-8 hours. Remove from the crock, strain, cool, and freeze.