Pressure washer - fault finding

[locky]

I've got  Karcher K4 Compact that gets lightly used, not every week or even once a month.  Used it for first time this year, worked as normal then it decided that the pump motor is always on and wont turn off when the lance trigger is released. Normally the motor is off until the lance trigger is pressed. No external leaks and good pressure when spraying. About 3 years ago it lost some pressure and started pulsing and I think also had same issue of always being on, so got new parts, cylinder and control head and it was back to normal at about £50 for these parts. What I'm trying to understand is what part makes the pump motor turn on and off, as dont want to sink another £50 into it, but also dont want to spend £150+ on a new one. From what you read the domestic Karcher washers arent that reliable but Nilfisk are probably no better.  Searched online but most throw them away when faulty, anyway I'll persevere and see if its fixable but dont really want to be replacing parts at £50 a time every few years.

[Amark72]

I had a similar problem with my Bosch Aquatak, I stripped it down and found the cut in/out switch was sticking,  so cleaned it out freed off the pin that activates the micro switch that signal the motor to turn on/off and greased up with silicon grease and was good as new.

Parts manual below.

https://www.google.com/search?q=karcher+K4+parts+diagram&rlz=1C1CHBF_enGB892GB892&tbm=isch&source=iu&ictx=1&fir=qsI4naOym5areM%2CCMBZ9UOnxsbVVM%2C_&vet=1&usg=AI4_-kQiAR_YQNlVfgMH8DbWB6gGfMZsrA&sa=X&ved=2ahUKEwjyten41IXwAhVXPcAKHQTWCskQ9QF6BAgXEAE&biw=1920&bih=1057#imgrc=ZwiU81OJEe6wnM

 

At worst have a go and break it then have to chuck it out anyway or get it working with out shelling out, worth a go.   

Mine was a pain to strip down to get to the pump. 

 

Good luck