Ben
Not sure if this is same, but when I bought my Powermax the spray from the jets was not constant, it was spluttering at times.
Someone on one of the forums had a similar problem and told me to buy a female connector and attach this to the male connector on your jet hose and run the pump for a few minutes.
I do this before every job and have not had a problem with intermittent pressure since.
ps Female connector cost approx £15.00
Hope this helps.
Richard Edwards