Sounds right.
The nozzles I am referring to are the ones fitted to whatever flat surface cleaner you get... it is vital to have these right, especially with such a low flow rate otherwise you just won't get the right clean.
If and when you look at replacing the pump, be looking at a minimum of an 11hp honda engine with a minimum 2500 psi and 15ltrs/min pump and this will be able to handle almost any situation you come across.
If you want to have a chat, call me on 07957 982525
Cheers
Andy