Sonny,
It could cause problems with the unloader, I usually suggest leaving unloader set at factory
specification and varying pressure using nozzles.
For example a 5.5 GPM @ 5000 PSI machine we sold yesterday delivered 5000 PSI with a 1505 nozzle,
and @ 2500 PSI with a 1507 nozzle.
The 5000 psi spike pressure is held between the gun and the unloader so the pressure between outlet
of the trigger gun and the nozzle is determined by nozzle size.
If you use a #6 nozzle your pressure should be 3000 PSI with no unloader adjustments needed, it will
spike between gun and unloader at the pre-set spike or unload pressure.
For your surface cleaner two 1503 nozzles would give you @ 3000 PSI, if it is a 3 bar surface cleaner
you would use three # 2 nozzles 1502's............
Hope this helps...............