Hello,
It sounds like one of the elements is faulty. You would need to replace the whole heater tank. There is an 8.5kw and a 9.5kw version. If you would like to call us on 0845 126 4141 we can ask further questions and supply you with the correct spare part. We keep most Triton Spares in stock.
NATIONAL SHOWER SPARES, July 2008