Sending off a guarantee card changes nothing.
Warranty is owned not by the manufacturer but by the vendor - the organisation you gave your money to.
A guarantee card is just a marketing survey and provides no extra protection.
If the kettle is still in its guarantee period and you have proof of purchase the ask the vendor what they intend to do about it (they are unlikely to have a repair channel so their only realistic option is to replace it).
The guarantee is not free - you pay for it bundled in with the price you paid and your only contract is with the vendor. Do not let the seller fob you off with talk of it being down to the maker.
Good luck...
Peccavi
January 2009