Want to know what the black Knob, I think called unloader valve is used

Is there a black adjuster knob on the end of the brass valve block on the pump ? if yours is like this try tightening it and loosen to see if valve unsticks .

According to epowerwash.com:
"The unloader valve diverts water flow into bypass when the trigger gun valve is closed. Unloaders may be designed to respond to either an increase in pressure or a change in flow. The unloader valve may also be used for variable pressure adjustment."

More information here:
All About Unloader Valves ePowerWash

That would be your unloader valve used for gun control. Allows system to go into bypass mode while the gun trigger is not depressed. This is already preset by factory specs usually a good idea not to move it unless you have a gauge to recalibrate it.

the pressure release valve is sticking

Im not sure you have replaced on the mechine and you say it worked for a weak so it sounds like a new problem . But i owen a few powerwashers and wash houses as part of my bussiness. The most likely things that will stop the pressure are eighter the valves in the water pump witch under the caps on the pump the cages are sometimes made out of plastic and peices of the cage can break of and stop the valve to not seal all it takes is one of them but if you remove the peice the mechine will work again . However it could be what is called the unloader valve . This is a valve located under the water pressure control knob it adjusts the pressure at the tip but also allows the water inside the water pump to recurilate in side the pump when the trigger is not pulled so the mechine won't over build inside the pump if its stuck in recuriculate you will have no pressure at the tip . Most of the unloader are not rebuildable but i fine if you remove them and turn the knob while spraying WD40 into them most of the time you can free them by turning the pressure control knob You have to play with it good luck

The pressure relief valve must be stuck. That is the part with the black knob were you adjust pressure. If it can't "unload" so tghe wagter has no where to ok, and then the pump will stall. You may be able to disassemble valve, soak in vinager or mild acid, rinse well and reassemble

If you have a black cap on the top of your pump, the unloader is under that. It is called a spill valve and they sometimes can be a real pain to remove. I usually take a drill and drill a 3/32nd hole in the top of the valve, screw a long screw into the hole and use pliers on the screw to pull it out. You may have to try several times before you get it out. If you don't have a black cap on the top I would need to know the model # of your machine to help.

There should be a big black knob off to the side of the pump. That is called an unloader valve and could either be sticking or is turned up to high. To turn it down turn it counter clockwise.

If it is sticking you should fix or replace it. If enough pressure builds up before it shuts down, one of the valve caps could shoot off like a bullet.

Hi:
Cleaning it is not enough. You need to make sure the o-rings are in good shape and grease it with a very very good waterproof grease. Here is a schematic of the pump. The unloader is parts 7 to 13 on D-2

First clean the unloader valve, then see if it will raise pressure, is the pressure control knob woking ok? let me know also check tank condesation vavle. Let me know if this helps or if you need more information. Thanks for useing fix-ya.Avid101