When you pull the trigger on your pressure washer, if the water pressure is good for a moment but then weakens, you have a surging issue. A few factors could be causing this problem. Generally, this means that the flow rate required by the pump cannot be supported by the water supply. Before calling a repairman, try troubleshooting the situation yourself. You might be able to save some money and hassle.
Remove the nozzle and clean it with a nozzle cleaning kit. You may have a partially plugged spray nozzle. If you cannot clean it well enough or if it is worn, you will need to replace it.
Check the unloader and repair or replace it. The unloader is used to relieve the water pressure within the pump whenever spray flow is blocked. It is generally located above the water inlet. It may be worn down or restricted in some way. In addition, air in the hose may cause pulsating. You can purge the air from the hose by pulling the trigger and allowing the water to flow.
Check the inlet hose and filter. You may have a restricted or leaking water hose. If this is the case, clean or replace the hose.
Secure an adequate water supply. You may have a cavitation or insufficient water. If this is not the problem, you may have worn pump packings. Inspect them and replace them as needed.
Inspect valves and clean or replace them as needed. You may have fouled inlet or discharge valves. The inlet valve allows water to enter the manifold. When the inlet valve closes, the plunger thrusts the water downward, causing the discharge valve to open and release the water. It is located on the discharge side of the pump. If these valves are fine, then your valve spring may be broken and need replacing.