Karcher pressure washer runs constantly when turned on and blows washer hose off, when handle depressed on lance. Is this a spill valve problem?

If you have a Karcher then you should always post your machines barcode.

full article on nozzles :
http://repairshed.blogspot.com/2013/09/pressure-washer-lance-nozzles-what-you.html

The spill valve operates at approx 20% higher than specified pressure washer operating pressure. If you have any lance issues then the pressure could be running higher than specified (machine running at same pressure as spill valve operation pressure)

your machine produces a fixed flowrate of water (maybe 8 litres per minute) and your nozzle is a fixed size. the diameter of the nozzle determines the back pressure. A piece of debris could further close your nozzle orifice and increase the back pressure. Using a new lance that has the wrong nozzle fitted can also cause this issue.

The karcher barcode is on a silver sticker and is usually 15 digits long. Example 156987400000123 is actually model 1.569-874.0 and serial number 00123....

try the machine with the lance removed from the gun.

buzzing is usually the noise made by the motor when it cant turn. if the pump start to pruduce pressure but the pressure builds up too high then the motor will stop turning... faulty lance or faulty spill valve (dump valve)

If you have a Karcher then you should always post your machines barcode.
The karcher barcode is on a silver sticker and is usually 15 digits long. Example 156987400000123 is actually model 1.569-874.0 and serial number 00123....

This is two things. One is the back flow check valve to the soap line is leaking. The other is the pressure switch on the output side of the pump.

First you have to do is try the machine without load. Attach everything as usual but do not attach the lance. Put on machine with water supply already on. If you close the gun the machine should stop. If you open the gun ( always with out lance)....the machine should start sending the water a bit far. If this is OK....then you have a lnance with a faulty, blocked NOZZEL.
NOrmally the machine stops when gun is released because there is a valve (Spill Valve) that actuates a electrical micro switch. This in turn closes off te elecreic supply...stopping the machine.
If with out lance your problem is still there....then the spill valve is faulty. AS I first said you must be sure that the nozzel is OK, so that you can blame the Spill Valve.
I raely service Spill Valves (Control Valves). I change with a new one. When open the cover using a TORX T15 screw driver....you locate the spill valve where there are 2 wires coming out. Some machines have the spill valve incorporated with the head and the intake and delivery valves unit. This I advize to change with new parts. These all in one heads are very good because at one go you change the spill valve and the other valves in one go.
Therefore in a few words you either have a blocked nozzel...or you have the spill valve faulty.
Also the delivery valves could be blocked...thus creating pressure inside and activating the spill valve to close off the electricity. You can also try to start the machine without gun and hose attached...but always with water being fed. NEVER put on a power washer without water being fed. And never store a power Washwer withpressure in it.
Fulltech.

The power washer stops when the gun is closed. This happens because pressure is exerted on a control valve (Spill Valve)...which in turn touches a micro switch and cuts electricity. Now most probably your machine is kickin in an out because the spill valve got faulty This happens when one stores away the machine with pressure still in it. NEVER store a power washer with pressure in it. The spill valve also gets faulty because left with soap and machine not rinsed. I rarely service spill valves...I change with a new one.
To locate the spill valve open cover (using a TORX T15screw driver)...and where you see 2 wires coming out...there is the spill valve.
Sometimes these machines have the spill valve incoporated with the head....in that case the whole head must be renewed. I also wish to tell you to try using the machine with out the lance. If all works good...then the on and off could also be comming from a faulty nozzel.
Regarding the Spill Valve...when it gets faulty...the machine also lose pressure. So in your case it is most likely that the spill valve is faulty.
Regards,
Fulltech.

Dear Sir,
The power washer stops when the gun is closed. This happens because pressure is exerted on a control valve (Spill Valve)...which in turn touches a micro switch and cuts electricity. Now most probably your machine is cutting out because the spill valve is getting faulty or stuck down and closing the micro switch. This happens when one stores away the machine with pressure still in it. NEVER store a power washer with pressure in it. The spill valve also gets gammed and faulty because left with soap and machine not rinsed. I rarely service spill valves...I change with a new one.
To locate the spill valve open cover (using a TORX T15screw driver)...and where you see 2 wires coming out...there is the spill valve. If you can manage to do this..you can try if you want to lubricate it by spraying SILICON spray. If you get it out..you use silicon grease.
Sometimes these machines have the spill valve incoporated with the head....in that case the whole head must be renewed. I wish to tell you to try using the machine without the lance. If it works correctly, then you have a faulty nozzel in the top of the lance. IMPORTANT...never run a power washer with water being fed!!!!
Regards,
Fulltech.

Dear davedulmage,
To see if the unit is OK....first you must switch it on without water and without high pressure hose and gun. If machinr works smoothly, try by attaching a water supply. Now run the pump with water coming out of the outlet. If also in this case all runs smooth, then attach high pressre hose with gun but without lance. Put on the machine with gun open(to reduce initial resistance) and when you see a clear flow of water coming out...close the gun. The machine should stop. In this case I am suspecting that when you open again the gun the machine will not work. So it seems that when pressure is built in the pump a fault is occuring in the Spill Valve or also called Control Valve. When the gun is closed and pressure built up, this spill valve contracts and switches the pump off. When the gun is opened, the spill valve extends, putting the machine on and closing a valve at the base of the spill valve. So in your case it seems that the spill valve needs to be renewed. A spill valve gets stuck by incorrect using of the pump. For example leaving the pump with pressure in it for a long time. Also it gets stuck by detergents and chemicals. Sometimes I lubricate Spill Valves with high quality silicon grease....but it is much more practical to change it. When a new spill valve is put in....always run the pump with no load. This by usiing the gun without lance or wands, resulting in low pressure. If all OK...add a lance or wand that you are sure it is good. One final thing....to get to this spill valve you must put apart the body and expose the pump. If you are not that good at doing this job...it is better done by a more knowledgeable person. But changing the spill valve is worth it....because it is cheaper than a new machine.
Regards,
Fulltech.

Dear mike husband,
One reasin for this fault could be a damaged lance or turbo lance. Try by replacing with new ones. If the problem is not solved, then the fault is due to a damaged spill valve. The spill valve could easily be damaged by using not suitable chemical or detergents. After using chemical detergents, one must always rinse the machine by passing pure water. The spill valve could also be damaged by leaving the machine for a long time with pressure in the system. One must never store such machines with pressure still inside. Always press the gun before storing.
Well the solution is to change the spill valve with a new one. In some cases even faulty suction valves can give this problem. But in the majority of cases it is the spill valve.
If you do not know how to fix this problem, it is better to be done by an expirienced technician.
Regards,
MG.

Dear jimbocom,
The problem is that the spill valve got stuck. When the machine is working and the gun is closed, a valve( spill valve) moves with the accumilated pressure and switches the machine off. So what happened is that when the spill valve did its job, it found no water...and remained stuck. This leaving the machine in an off position. Service and lubrication to the spill valve must be done or completely replacing with a new spill valve. In my opinion you have no serious damage, but this job must be carried out by an expirienced technician.
Regards,
MG.

I had the same problem - good water inlet pressure, no output pressure, even though the lance and handle seemed to be clear and working find.
I found that the electrical switch wasn't being operated correctly by the spill valve and wasn't turning the motor on/off correctly.
Inside the plastic electrical box there is a small white device that presses against the micro switch assembly. Carefully adjust the allen screw perhaps 1/4 turn out or 1/4 turn in to obtain correct operation of the microswitch - you will hear the micro switch clicking in and out when re-assembled. I'm sure they must have a rig to check correct positioning of this screw in the factory!
Hope it helps - mine is working find now and saved me buying another!