Small Engine Troubleshooting Problems? Ask a Mechanic Now.
There is a relief valve in the system, but before diving into the pump, have you removed the trigger gun and checked the trigger and nozzle for debris? Sounds like the outlet is plugged! If we need to go further, I need the model number of the unit, so I can find breakdown of the pump. If you have manual showing parts, look for relief valve and spill/unloader valve.
!! Have you removed the outlet hose from pump and turned it onto see if water flows? If not,go back and check the pump manifold for debris!