nH means 'not heating'. I had this problem, the water was heating however. There is a temperature sensor inside the door (a thermocouple) it is attached right next to the soap dispenser in the middle of the door, mine had come detached from the door, I put it back on and it was fixed.
WARNING: Wires in the door, and throughout the entire machine carry 240V mains power. If you don't know what you're doing, you should leave it to someone who does.
In the manual that came with the dishwasher, it says nH is 'unit not heating': if it IS heating.. Allow time to heat water (up to one hour), connect to hot water supply. If it's NOT heating: Contact service division.
Chris Conlan, May 2008