F&P NEMO upper spray arm not spinning?

it is 3 years old. The machine has always delivered a very poor quality wash (day 1) especially the upper rack dishes. The spray arm at the top doesn't spin. I have had the repairman out many times but he has not been able to fix the problem despite replacing many expensive parts (pump) has made no difference. F&P, being the unhelpful company they are, have lost interest and I am stuck with a lemon, any last ideas before I pour petrol over the damn thing and set fire to it?