hi, lets see if i can help. if you have lost your pressure, i would check to make sure that nozzle on the end is not plugging up. if this is clear and you are getting water out the end of the gun then the problem will be the unloader valve on the pump, it is either sticking are it is broke, on this model the unloader will be on the top of the pump, sometimes they are easy to remove and sometimes not,
Can you describe what the unloader valve should look like because I had a small engine repair gentleman look at it and he could not identify it on this model. He said it was not like most other models where you could easily see it.
it should be on the cylinder head on the pump, there should be a pipe plug that screws into the head on the pump, when you remove the plug the unloader should be inside,it will be about a inch long it may be hard to remove if it is stuck, you may need to spray some wd40are other lube and take a pair of needle nose pliers work it around until it frees up. sometimes it comes out easy and sometimes not.