Go to eBay's contact page and get them to phone you - you generally only have to wait a couple of minutes and explain the situation to them.
Don't post back the coffee machine. Once the seller has it back, you have no proof if they say it's not faulty, plus you have no coffee machine and may have to pay further P+P to get it back!
You will also be paying to post it back to the seller, don't forget
EBay's complaints team will tell you what to do. They are experienced in these matters and usually find in favour of the buyer.