Boiler's been broken for a week and landlord still hasn't sorted it?

Boiler broke last Sunday and despite calling our land lord everyday to get it fixed, he still hasn't; he'll say he'll come over the next day, so someone stays in (missing lectures) to wait for him and he never shows, doesn't even call to say he's not coming. The house is now so cold we can see our breath and have to wear coats to bed... What should we do? What are our rights as tenants?