What do I have to do to repair my electric pressure washer?

I have a Simoniz S1900 Pressure washer which only mildly boosts the water pressure when power is turned on. (It worked fine when I first purchased it 3 years ago.) Troubleshooting the problem led me to disconnect the "pressure hose extension" which carries the water from the outlet at the bottom of the unit to the inlet on the hose reel. When I hit the power button the pressure of the water coming out of the now connection-free outlet at the bottom of the unit was great, but of course of little use. When I re-attach the pressure hose to the bottom outlet and leave it un-attached at the reel, the water pressure drops way off. I get the same result when I attach the reel hose directly to the bottom outlet. I've blown out the hoses with an air compressor but still no change so I'm thinking that there is something happening internally when a hose is connected at the bottom outlet. Any thoughts that may assist me in resolving the problem?