Do not ask the seller to send a courier. If they do, you won't have a tracking number to prove delivery, and won't be able to make any claim through eBay if you don't receive a refund.
Always process returns through the resolution centre. If an item isn't as described, use eBay's money back guarantee. Assuming that the Hoover was sent from within the UK the seller will be required to send a prepaid return label. (If it doesn't cover the weight you may need to phone eBay customer support to get it changed for one that does.)
The rules and time limits have changed recently - you can read the full terms and conditions here: http://pages.ebay.co.uk/help/policies/money-back-guarantee.html
Follow the instructions carefully and, if necessary, escalate the case for eBay to step in. Don't agree to close it until the matter is resolved.
p.s. do you mean an actual Hoover, which is a trade name, or are you using it as a generic term for a vacuum cleaner? Be sure to be accurate when opening a case.
