challenge xtreme washer ?

I have a Challenge Xtreme 1800w Upright High Pressure Washer.The proplem is fluctation in water pressure,this even happens when all hoses are removed so the pressure is coming straight from this pump.the vonly way I can describe it is as if it is "hunting"ie high pressure then a ver short pause then back to high pressure.

thank you for any advice you can give me with this proplem,also can you recommend a more suitanble machine for home use.

Regards Mr A C O`Meara

tony o`meara
November 2010