replacing my 8.5kw shower?

I think my triton T80i shower needs replacing because when the unit is switched on, the power light no longer lights up and the water runs cold (although when the power selector is set to high(2 red bars) and the temperature control set to max (10) the water does get slightly warm.

Firstly, am i correct in thinking the shower needs replacing?

Secondly, the electric power supply cable is 6mm, less than 18 metres from the fuseboard, and wired to a 40 amp rated mcb. Will i be able to replace the shower unit with a 9.5kw or will i have to stick to a 8.5kw?