If the seller represented to you that the furnace that you were buying was new and it was not and you paid money for it as though it was new, then you had the right to cancel the check for its payment under the law. What needs to be done is to return the furnace if you have it in your possession.If the seller has it, write the seller stating he or she is to keep it and you are cancelling the purchase based upon the seller's misrepresentations to you as to the furnace's age.