Ring triton in Maynooth, they will have the part and can recommend someone to fix it, they are fairly reasonable - you may be still under warrenty. I've had one of these repaired, the inside looked pretty straightforward, just a watertank, element, pump and a few wires. But the water and electricity thing would put me off doing it myself.
If the water is heating to some degree it may not be the heating element but the regulator or thermostat, phone a self employed local plumber who should tell you how to check the fault, This is a very popular shower and you may find the plumber has some spare parts himself. It is safer to let a plumber or electrician replace the part, DIY is not a good idea on an electrical shower.