Karcher k4 won't turn on.

https://www.sosav.com/guides/cleaners-hp/karcher/karcher-k4-ecologic/wheels/

Spudger to remove the plastic hub, K4 K5
..

check gfi plug for failure

Probably pickup is plugged, try (with safety goggles on) blowing back through the pickup tube.

Karcher 4 650 Operating Instructions Manual

Sharon, Check the attached links,instruction and guides, Good luck
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How to FIX Karcher pressure washer
Karcher North America Home Garden Online Help

David, pressure relief valve, sticking, defective.

check out here and click on product manuals http://www.karcher.co.uk/uk/Products/Home__Garden/Pressure_washers/11806610.htm

I fixed mine works good too, watch my video step by step i put it on youtube
http://www.youtube.com/watch?v=UFXSLOBL0Mg