Recently had similar problem. Unscrew the pressure valve completely and replace the pin. About £12 from Ashby's. Also found that air in the system is a big contributor to pressure loss in this system. Bleed system for 30 seconds after each refill. You'll notice the difference at the wand tip straight away.
If you're mildly technically minded - it's worthwhile taking the head off the pump and inspecting for signs of cavitation in the alloy head, the condition of the rubber seals and removal of any foreign matter.
Keep your chemical usage to a minimum and install a water conditioning device. Doesn't have to be a water softener. Around £70 will get you a fit and forget central heating type electro magnetic scale reducing box of tricks (about the size of a big box of matches and draws less than 1 watt) with two long 'antennae' that coil in opposite directions around the main inlet pipe. I noticed a massive difference in a very short space of time. (especially good if you're using the V2). A cheaper version involves getting a long nyodium? (not the right spelling) magnet, clamping metal along one side and strapping the other side to the inlet pipe - this will set you back about a fiver. Both systems will make the molecules in the water (and of the scale in the water) all face in the same direction thereby - somehow keeping everything in solution and not coming to rest on surfaces. If you google this application there is someone out there that promotes this as a way of increasing fuel economy
in your vehicle.
If you're using the BIG heat of the V2 then I'd advise installing a second magnet after the heat exchanger.
Hope this all helps
Alan
