I've just fixed my smeg dishwasher that was showing error code e8. This error indicates that the 'alternate valve' is misbehaving. Thought that others might like to know how to fix it...
The alternate valve is in the bottom of the machine roughly in the middle (turn it on it's side and pop off the plastic bottom plate). I removed the valve - that required taking off two hoses and unplugging the connector. The valve seems to have leaked a bit and had gunk all over it. I took it apart and cleaned it (there are some plastic gear wheels and a motor that pops off). There is a micro switch which detects the rotation of the valve. The switch is a 'normally closed' type and wasn't working. I removed it and carefully eased it apart and cleaned the contacts. Put it all back together and now the dishwasher is working again!