Thanks ladies! I had a brainwave last night in the middle of the night that I was sure the extended period was 4 years and the initial manufacturer's warranty was two years (not one as DH had insisted). Checked the paperwork - DH has never been so happy to be wrong!
They're going to come out Wednesday to have a look at it. If, as suspected, it's really truly buggered then they'll replace it with a new one!
Phew! So relieved at having a bit of time before we absolutely *have* to spend that money. Will definitely keep the recommendations in mind for when the time comes though thanks!