Have you got good water mains pressure Red?
It pressures up to the handle but when i press the trigger it trickles out.
Had the same problem here when feeding from a header tank,
we had to have a tap fitted at the feed point to the house as the pressure from the tank was not good enough,
Karcher has long gone and have a stihl washer now that works well but not as well as the Karcher did,
bob.