I have a KEW 240v Power washer, which is approx 20 odd yrs old. It has always worked 1st time on the odd occassion when it is taken out for use. However, now it will only work perfectly so long as you start it with the trigger of the lance depressed, and only switch it off and on with the main on/off buttons. The problem is that it continues to blow the 13amp fuse everytime you release the trigger on the lance. I have run it without the hose attached and it works, I have run it with the hose attached and it works. I have replaced the oil in the pump and made sure that all internal workings are free from rust and dirt. The pump is of all brass construction and the motor is perfect.
The lance has been thoroughly cleaned and works perfectly when cleaning the slabs but as soon as you release the trigger to cease work the unit strains momentarily and immediately blows the fuse.
I have used it via the HD extension cable and direct from the socket which excludes any outside problem.
The problem seems only to occur when the trigger is released. The unit works perfectly but being unable to release the trigger and having to switch it manually at the unit, as you can guess, is driving me potty....

Davy Mac, March 2009

Pecavvi. Thanks alot for your advice. Will investigate more on Monday.
Cheers mate...

Davy Mac, March 2009

Apparently they're called Unloader Valves
Lots of pictures on Google Images

May not be the switch - could be siezed up mechanics failing to operate the switch.

Peccavi, March 2009

No idea Davy Mac - never been inside a pressure washer...

It will probably be screwed into a pressure reservoir vessel and have two wires in series with the on/off switch on one side and the motor on the other side.

Live...On off switch...Pressure switch...Motor...Neutral

And I strongly suspect that when you test it it will be permanently closed

Still guessing...

Good luck...Take care...

Peccavi, March 2009

peccavi. Thanks for that reply. Tell me! what does this pressure switch look like or where is it normally located on a pressure washer?

Davy Mac, March 2009

All guesswork....

The job of the motor is to create pressure to drive the water flow - the motor runs until a pressure switch says stop - you squeeze the trigger, water flows, the pressure reduces and the switch asks the motor to run.

If the pressure switch were defective and not turning the motor off when it should, then the tendency would be for the motor to become overloaded possibly blowing a fuse.

With a defective pressure switch, turning the machine on with the trigger already pulled would mean the motor never gets up sufficient pressure to need to stop. If you release the trigger and stop the flow the motor has no control device and continues to run on until the fuse pops.

Possibly a defective pressure switch/circuit

Peccavi, March 2009