When you purchase a product, generally the manufacturer via the shop offers a 12 month guarantee. Some manufacturers and/or shops offer longer or extension options too.

If the product you purchased breaks down and is subsequently replaced by either the shop of manufacturer, you are still in a contract of sale which began at the time of purchase. Under that contract of sale you received a 12 month guarantee that is fixed from the date of purchase and can only be extended at the manufacturers’ discretion.

If on the other hand you had been offered a refund and then purchased a replacement, you would then be entitled to a new 12 month guarantee starting at the time the replacement is acquired. In essence, you haven’t lost out; you were given a 12 month guarantee, which is still in force, in addition, you would now have the luxury of a new vacuum cleaner, which hopefully will last a lot longer.

So yes, John Lewis are right