PUMP CYCLING

A water leak downstream from the pump can cause your pressure washer to cycle on and off.  

The trapped pressure unloader valve is designed so that it uses the pressure trapped in your hose,  to keep the bypass open. 

When the pressure in the downstream portion of the system drops to the set pressure of your unloader valve, the bypass circuit closes, allowing pressure into the hose.  

Under normal conditions the pressure is trapped in the hose until the trigger gun is pulled.  When pulled, the drop in pressure closes the bypass valve and allows pressure into the pressure hose.  As long as the pressure does not exceed the unloader setting, the bypass circuit remains closed.  The bypass circuit is water the pump is pumping, being sent back to the low pressure side of the pump.

When you have a leak the hose pressure gradually bleeds off to the set point of the unloader  When this happens, the hose instantly pressurizes, which causes the bypass to open again.  

Depending on the leakage this could happen every second or so or only occasionally.  In any case it's not good for your system and the problem should be corrected.  Find out where the water is leaking and fix it.  If it's the trigger gun, replace it.  

If it's leaking quick connectors, replace the o-rings.  

Check here for more information on different types of unloaders and how they work.