Combine the cider, sugar, orange juice, orange zest, cloves, cinnamon stick and vanilla bean in a saucepan over medium-high heat. Bring to a simmer and cook just until the sugar dissolves, 2 minutes. Transfer the mixture to the slow cooker. Add the pears, and then cover with a lid and cook on low2 hours, turning the pears halfway through.
Remove the pears using a slotted spoon and transfer to serving plates or a shallow dish. Carefully strain the poaching liquid back into the saucepan and reduce the liquid by half until thickened and syrupy. Pour the reduced sauce over the pears and chill in the refrigerator an additional 2 hours or up to 2 days.