SMEG df612SE diswasher error E8

Hi,
I’ve had our dishwasher for about 18 months and we’ve had the repair man out 4 times now all covered by the guarantee. Its worked for about 6 months ok but is now throwing up the E8 error – it starts to wash from the top arm only and then switches itself off after 5 minutes and empties itself. I’ve checked the valve which switches the water supply between the 2 arms and the valve was stuck in the position where water isn’t fed to the lower arms. So i’ve tried manually openeing the valve manually andthen disconeecting the power to the motor. Now at least water goes to both arms but it still switches itself offafter 5 minutes and posts the e8 error still. I thought it may now need to be reset but i can’t get the reset technique posted to work.They all mention pressing the programme button 4 times with the door open until the 1 and 5 lights come on? My machine has 5 programme buttons does it matter whiuch one i press? Also none of the lights will come one with the door open – is it just cos i’m not doing it right? I know I should call out the engineer but money is a bit tight so i’m trying to avoid it if possible – luckily my dads an electrical engineer so he has some idea bout these things.

I’d really appreciate some help?

Cheers,

Mark