When it pulses, the plastic cylinder head will be cracked. Cost around $65Well, all I can say is that I have a Karcher and a Gerni, both roughly same age and usage hours, and the Karcher has carked it already, whereas the Gerni is going fine.
The Karcher pulses constantly and has no pressure.
I have fixed it by remelting the crack with a soldering iron.
Run the Karcher with all covers off and you will see where the crack is
Disassembly is easy, check out Youtube