Karcher pressure washers not pressurising

k297 no pressure, trigger works, as it lets tap pressure water come out, but thats it. it humms, i stripped it down, cooling fan shaft worn flat (bit like you find on hp / wk condenser dryers, so whipped that out, turned it back on only to get a moments worth of “clatter” noise and jet, before going back to a more muted hum, and no pressure. any ideas where to look? the vans getting very dirty now with all this pollen about.

and its 2 1/2 years old