Same issue here, same model, my smeg 12043 DWI612C dishwasher gets stuck on the wash cycle.
Water comes in and out, the soak cycle (lamp one on the left lit) works fine, and I've performed multiple resets (power on, press mode button 4 times in 3 sec, lamp indicators 1 and 5 light, power off for 20 seconds, power on, run rinse cycle to completion, drains to empty).
However any of the wash cycles simply run on and on, periodically stopping briefly and starting again with a beep-beep. I've let it run 10hrs to see if it will snap out of it. Perhaps coincidentally this started occurring when I had some hot-water boiler issues where water wasn't heating at the boiler. At that time the dishwasher started it's prolonged cycle and I thought it could be something to do with heating its own water. The boiler is now fixed but the problem is still occurring.
The dispenser does open, the wash is running with hot water (dont' know if it's self heating or not), and there are no error codes indicated by the display lamps. The endless cycle it's running is has bubbles, indicating it that it is the wash rather than rinse cycle that is looping, and the water is hot.
Any suggestions welcomed.
Simon, September 2011