the machine makes a loud knocking or rattling noise when it's running.

Diagnosis

The loud knocking or rattling noise in your Craftsman CMEPW1900 is a classic symptom of pump cavitation. This occurs when the pump is unable to draw a consistent volume of water, creating low-pressure vacuum pockets that collapse violently against the internal pump components. This "implosion" effect manifests as a metallic rattling or a rhythmic hammering sound that can be felt through the chassis of the machine. This typically happens because of an air leak in the suction line (the garden hose connection) or a restricted water supply. If the pump sucks air instead of water, the internal pistons and valves are not lubricated or cooled, leading to rapid wear of the seals and potential cracking of the pump manifold. You can confirm this by checking if the spray pattern is "pulsing" or "spitting" rather than providing a solid, continuous stream of water. If the noise persists even after purging, you may have an internal valve failure or a foreign object lodged in the inlet filter.

How to Fix It

Follow these steps precisely to purge the system and stop the cavitation:

1. Turn the power switch to the OFF position and unplug the unit from the electrical outlet to prevent accidental startup.
2. Disconnect your garden hose from the water inlet of the pressure washer. Inspect the rubber O-ring inside the female coupling of the hose; if it is pinched, cracked, or missing, replace it immediately to ensure an airtight seal.
3. Reconnect the hose and tighten the coupling firmly by hand. Avoid using pliers, as over-tightening can crack the plastic housing on the CMEPW1900.
4. Fully open your outdoor water spigot. Ensure there are no kinks in the garden hose that could restrict flow.
5. Before plugging the machine back in, squeeze and hold the trigger on the spray gun. Keep the trigger depressed for 30 seconds to allow water to flood the pump head and push out any trapped air pockets.
6. While still holding the trigger, plug the machine in and flip the power switch to ON.
7. Continue holding the trigger until the rattling noise disappears and the water stream becomes steady. Once the noise stops, release the trigger and then resume normal operation.

If That Didn't Work

• Inspect the Inlet Screen: Unscrew the water inlet fitting and check the small mesh filter screen. If it is clogged with sediment, algae, or calcium deposits, the pump cannot draw enough water, causing cavitation. Clean the screen with a soft toothbrush and white vinegar, or replace the filter if the mesh is torn.
• Check for "Air-Lock" in the Hose: Some high-diameter garden hoses trap air bubbles. Disconnect the hose from the pressure washer and run the water through the hose into a bucket for 10 seconds to clear all air before reconnecting it to the machine.
• Verify Pressure Regulator Valve: If the rattling occurs only when you release the trigger, the internal bypass valve may be sticking. Cycle the trigger rapidly 10-15 times to clear any debris from the valve seat.
• Inspect for Pump Seal Failure: If you see water dripping from the bottom of the pump housing while the machine is running, a seal has failed. This allows air to be sucked into the chamber. In this case, the pump assembly must be replaced as the CMEPW1900 pump is generally a sealed unit and not serviceable at the piston level.

Heads Up

• Never Run Dry: Never start the motor without the water supply turned on. Running the pump dry for even 60 seconds can overheat the seals and permanently damage the pump's efficiency.
• Winterization: Always use a pump protector or drain all water from the unit before storing it in temperatures below 32°F. Frozen water will crack the pump manifold, leading to air leaks and cavitation.
• Water Quality: If you are using water from a rain barrel or pond, you must install an external pre-filter. The CMEPW1900 is designed for clean potable water; small particles will shred the internal valves.
• Hose Length: Avoid using garden hoses longer than 50 feet. Excessive length can cause a pressure drop that prevents the pump from getting enough volume, triggering the rattling noise.