How do you reset a karcher pressure washer

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

The test / reset buttons are for a Ground Fault Interrupter built into the cord / washer. This device will help prevent deadly electric shock in the event of a malfunction - it is the same technology used in "GFI" electrical outlets located in bathrooms, outdoors, basements, etc.

You should have this serviced - or replaced before using.

Good luck!

Are the threads on the end ok, if not it sounds like the bypass unloader valve is at fault.
Thanks qwashers

it;s normally a switch interrupter must replace with actual with for motor protection.

unit may have either a bad power switch or stuck flow switch normally located at the inlet of pump inside where you hook up the garden hose

Your pressure washer is either not fitted with a run/stop device in which case like mine you have to switch off within a few seconds of closing the trigger. Check your model features?
The humming noise is the motor stalled out against the pump because there is nowhere for the water to go. The shutoff is caused by the safety overload switching off after overheat.
Or, it has a pressure operated run/stop which is not working. Because water and electricity don't mix, I would suggest getting more specific help. You can download Karcher manuals /spares lists online from Karcher specialists but remember electricity is the silent killer.

But water comes out the end right? just under hose pressure only I bet. I have one of these units and every time I think it has gone bad I manage to find the problem. This unit not only has the switch on the front that needs to be on but it also has a safety switch on the plug where it plugs into a wall or extension cord. The last time I thought mine had gone bad it had actually blown the fuse. the unit was plugged into an outside outlet via extension cord. It just so happens that that is an GFCI outlet. I think the wife got water on the extension cord and that caused it to blow. So check:
The power switch on the front The safety switch on the cord, The outlet it is plugged into
Usually, for us, it is the button on the cord when it is plugged into an extension cord it always gets the test button bumped which shuts it down.

can be multiple issues loose wires at switch, is termo protect if overamps or pressure switch sticking

Under the top cover there is a micro switch that sometimes dislodges
This switch is for auto cut off when you release the trigger

They are sensitive to large extention cords. My father in laws pops reset when a small cord is used. If internally shorted- motor will continually pop the reset even plugged direct to outlet. Check voltage at outlet.