hi what you need to do is remove the right hand side panel (disconnect from mains) you should see a round heater that water flows through. disconnect the white connection on top of the heatr. you need a multimeter to check if you have 240v from this connection. to do this connect the multimeter to this connection ie put the red probe of the multimeter to one wire and the black probe to the other. now reconnect to the mains(be careful) select a quick wash on dishwasher and start.after about 5 mins you should get 240v on multimeter if you do then the heater has failed if you dont you need to replace the control panel.ie the pcb which is behind the buttons you press to select wash cycles.hope this helps(ps im not responsible if you electrocute yourself) this should not happen if you have common sense.
