The Bahama's have been an "issue" within the industry since their launch, it would unfortunately seem like your diverter valve has bitten the dust and I would recommend replacement... Although depending on your financial situation, a replacement boiler could be worth the spend if you require a reliable heating and hot water appliance...
Over the past year I have removed about 30 of these units due to reliability issues, it would seem as though you either get a good one, or a bad one... Some I've worked on never seem to give any problems whatsoever, yet others seem to always have visits with the doctor.
GasAid.co.uk
December 2006