The tech is an idiot. Get a new one.
The pump is rated at 4 GPM at 4000 PSI. That is what it's normal discharge is when the motor is running and the pump is turning at full RPM's. When they measure volume, the tip is taken out and put in a bucket. That way there is no theoretical restriction to keep it from full capacity. When this is done, ideally the pressure should read zero, and the flow should still be there. The only way our pumps develop pressure is by the restriction of the tip. So I will put it another way, Your pump is rated at 4 GPM. whether it is at 0 PSI or 400 psi or 4000 psi. It makes no difference whether there is a tip in it or not. The 4000 PSI is the maximum pressure that the pump is able to deal with on a normal operating basis. For your pump it is expected that you will use a number 4 tip to achieve the 4000 PSI.
Most of the contractors on these boards have hot water machines that use a General or Interpump TS2021 pump. It is rated at 5.6 GPM and 3500 PSI. Most run it, and a lot of pressure washer manufacturers run it at 5 at 3000 PSI. These pumps last well are not overworked. But if you put a large engine, and a larger tip in, you can get the full rating.
There is a caveat, or warning, you can redice pressure, but DO NOT reduce water flow, that will cause the pump to heat up and the seals to fail prematurely. That means, that no matter how hard you try, after the seals fail you will only get a lower pressure, depending on how bad the failure is.
Scott
