Outdoor Power Equipment and Small Engines - Karcher K 390M

First let me say hi from Belgium.
Can someone assist me with the low pressure problem on my Karcher 390M pressure cleaner. I have read many posts on this site and others reffering to the unloading valve, my cleaner worked fine then decided to not give any pressure. I have located the parts list via one of the posts in this forum but do not know which part is the unloading valve so that i can check it out. The parts list was located at http://m-and-d.com/pdfs/Karcher/K-390M-330M-Plus-Parts-List.pdf
can somebody post what i need to check or replace to solve the problem.
Forgot to add when first posting that when the gun trigger is not pressed that the pump has also started to cycle on and off on its own (as if you are pressing the gun trigger on and off)

I'm not familiar with electric washers, but since the motor comes on upon demand instead of running constantly like a gas engine, I don't see any reason for it to even have an unloader valve. I would suspect pump problems.