Graham FisherBy Graham Fisher

Updated November 2026

Simpson pressure washer parts are easiest to find when you know your model number, the engine or pump type, and which component has failed. This guide walks you through identifying the right part, sourcing it, and handling the most common replacements. Most owners can handle hoses, nozzles, unloader valves and spark plugs without special training.

Find Your Model and Pump Information First

Before you order anything, locate the data plate on the frame or engine shroud. You are looking for the model number, serial number and rated GPM and PSI. Simpson units are often built with pumps from other manufacturers, so the pump brand and model may be listed separately on the pump housing. Write these down, because a part that fits one model year can differ from the next.

Shopping for one? See our guide: 7 Best Green Work Pressure Washers for Home Use (2026).

If the plate is worn, check the owner’s manual or the original packaging. Matching the pump specification matters more than matching the frame. A replacement unloader or pump head with the wrong flow rate can overpressure the system or starve the pump.

Identify the Failed Component

Pressure loss, leaks and no-start problems each point to different parts. Work through the symptoms before buying:

  • Pulsing or weak spray: inlet screen, check valve or unloader valve
  • Water leaking at the pump: pump seals or O-rings
  • Hose bulge or drip at a fitting: high-pressure hose or quick-connect
  • Engine turns over but won’t run: spark plug, fuel filter or carburetor

Our article on Why Does My Gas Pressure Power Washer Lose Pressure? 6 Causes and Fixes covers the diagnostic steps in more detail, and it is worth reading before you replace anything expensive.

Source the Correct Replacement Part

Search by model number first, then cross-check the part number against the parts diagram in the manual. Compare the thread size, orifice size and connector type. Hose fittings are a frequent source of mismatch: a standard garden thread and a pressure-washer quick-connect look similar but will not seal together.

Part What to check
Nozzle tip Color code and orifice angle (0°, 15°, 25°, 40°)
High-pressure hose Rated PSI and fitting type
Unloader valve Matches pump model and GPM rating
Spark plug Gap and thread size listed in the engine manual

Replace Common Parts Safely

Always shut off the engine, disconnect the spark plug wire and relieve pressure by squeezing the trigger before you touch any high-pressure component. Then follow this sequence:

  1. Let the pump and hoses cool if the unit was recently running.
  2. Remove the hose from the spray gun and the pump outlet.
  3. Note the orientation of the old part, and photograph it if needed.
  4. Install the new part with the sealing washer or O-ring supplied.
  5. Hand-tighten, then snug with a wrench. Do not overtighten brass fittings.
  6. Run the unit briefly with the nozzle removed to check for leaks before spraying.

Replacing an unloader valve or pump internals involves higher pressure and tighter tolerances. If you are not comfortable with that work, a qualified small-engine or pressure-washer repair shop can handle it. Safety note: never work on a pressurized line, and wear eye protection when testing.

A quality set of nozzle tips in the standard color-coded sizes makes it easier to match flow and angle when a tip wears out. View on Amazon

A thread sealant tape rated for pressure-washer fittings helps prevent drips at connectors after you reassemble. View on Amazon

Common Mistakes to Avoid

  • Ordering by frame model alone, without checking the pump and engine specs.
  • Mixing garden hose and pressure-rated fittings, which causes leaks and can fail under load.
  • Installing a nozzle with a smaller orifice than specified, which can strain the pump.
  • Skipping the leak test after reassembly.
  • Reusing worn O-rings or washers instead of replacing them with the kit.

For hose selection specifically, see Hose Pipe for Pressure Washer: How to Choose the Right One (2026).

FAQ

Where do I find the model number on my Simpson pressure washer?

Look for the data plate on the frame or engine shroud, which lists the model and serial numbers. The rated PSI and GPM are usually printed there as well.

Can I use a standard garden hose fitting on a pressure washer?

No. Garden fittings are not rated for pressure-washer output and can fail or leak. Use fittings specified for high-pressure use.

When should I call a professional instead of replacing a part myself?

If the problem is inside the pump, or involves the unloader valve or high-pressure seals, consult a qualified repair technician. Improper internal repair can cause sudden pressure release and injury.

Conclusion

Start with the model and pump data, then diagnose the symptom before ordering. Matching the part number and fittings to your unit prevents most mistakes. For anything involving internal pump work, a professional repair is the safer choice.

Ready to choose one?

Graham Fisher

About Graham Fisher

Graham Fisher is part of our editorial team and reviews and edits our non-vacuum cleaning gear guides, checking product details against manufacturer specifications and owner feedback.