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How do I know if my pressure washer pump is bad? What pros say

A pressure washer is a useful tool that allows you to clean your patio, driveway, car, and other objects effectively. However, wear and tear over time can affect the performance of your pressure washer. One of the most common parts of a pressure washer to malfunction is the pump.

How do I know if my pressure washer pump is bad:

Several indicators will show a faulty pressure washer pump. The most common is a leak, pulsating output pressure, and low output pressure. Leaks are often caused by a worn or damaged pump seal. A pulsating pressure indicates that there is not enough water in the pump. Low pressure is generally due to worn O-rings or a dirt blockage at the pump inlet.

This article will provide you how to diagnose a pressure washer pump fault easily. I will list the indicators that point towards a faulty pump and the reasons behind pressure washer pump failure.

Faulty Pump indicators

Here are the most common pressure washer pump failure indicators:

1. Faulty Pump indicator: Leaks

Leaks are probably the most common problems associated with pressure washer pumps. Leaks are often caused by a damaged or worn seal. A leaking indicates a worn O-ring or gasket. Replace the old gasket with a new one to fix the leak. A leaking cylinder head or inlet/outlet elbow is often caused by frozen water inside the pump. Before the winter hits, you need to drain all water in the pump. Else it will expand and damage the plastic parts.

To identify leaks, remove the case of the pressure washer and turn the water on. Do not turn on the motor or engine with its case removed. Water coming from the hose will run through the pump and indicate the area from which the leak is originating.

2. Faulty Pump indicator: Pulsating output pressure

The main reason for the output pressure to pulse is an insufficient inlet water supply. In the case of an electric pressure washer, this results in the motor restarts. Remove the inlet filter and clean any blockages. If this is not the cause, there can be a blockage in the pump, or a leak from the cylinder head can also cause the pressure to pulse.

3. Faulty Pump indicator: Low output pressure

A pressure washer not producing enough pressure also indicates a fault in the pump. Low pressure is due to a worn-out O-ring. Or a rubber gasket that seals the inside of the pistons and valve. To fix the issue, replace the worn O-ring. If the seal is fine, low pressure can be due to dirt blockage. To restore the machine’s pressure, clean the filters and remove the dirt and debris that prevent the adequate supply of water to the pump.

How do you test a pressure washer pump?

To troubleshoot or test a pressure washer pump, turn on the pressure washer. Use the pump problem indicators to diagnose the issue. Different types of problems arise because of the failure of different parts in the pump. The table below will help to diagnose and analyze which part of the pump is causing the problem. Once you have tested and found the root of the problem, use the table to fix the problem.

How to fix
No pressure
Pump inlet valve damaged
You need to disassemble the pump and clean the inlet valve. If the problem still occurs, you need to replace the inlet valve.
Unloader valve damaged
To fix this problem, adjust the unloader screw. Also, check for damaged seals and springs.
Inconsistent pressure
Pump inlet valve damaged
Sometimes we receive pulsing pressure from the washer outlet, which means that pressure gets high and low constantly. This problem can be fixed by cleaning or replacing the inlet valve.
Faulty Pump
Replace the pump.
Air sucking pump
To fix this problem, turn off the washer and release the pressure inside the pump by squeezing the trigger gun.
How to fix
Water leaking pump
Worn or damaged seals
Change the seals.
Excessive Noise
Low level of oil in the pump
Disassemble the pump and check the oil. If the level of oil is low or the oil is cloudy, remove the old oil and refill the oil tank.
Oil leaking pump
Damaged seals, gaskets, or pistons
Disassemble the pump and check the seals or pistons. If they are worn or damaged, replace them.
Loose fittings
Oil may also leak due to loose bolts and fitting of the pump assembly. Check the pump assembly and tighten it if it is loose.
Low pressure
Insufficient water supply
Ensure adequate water supply to the washer by unkinking the hose or using a hose with a large diameter (3/4 “recommended).
Inlet filter blocked due to dirt and debris
Cut off the water supply and clean the filter.
Worn-out nozzle
Change the nozzle and make sure that you use the correct one.

Why does the pressure washer pump fail?

The life expectancy of all pressure washer pumps is pre-defined. The reason for pressure washer pump failure is not always natural wear and tear. A faulty unloader valve, cavitation, and water overheating can be some other big reasons behind pressure washer pump failure.

● Cavitation

One of the more common problems that occur because of low water supply pressure is cavitation. Air cavities, or air bubbles, form inside the water supply and can cause a loss in capacity and water pressure and a drop in efficiency. The pressure washer becomes noisier and vibrates more when the water inside the water supply becomes saturated with air cavities. The cavities leave low-pressure areas and pass into a high-pressure area. Cavitation can even cause a small explosion that damage the pump.

Cavities are formed for different reasons. The most common reason for cavity formation is insufficient water supply. The water supply flow should always match the Gallons Per Minute (GPM) rating of the pressure washer. Vaporization is another cause of cavitation in the pressure washer pump. It occurs due to the high temperature of the water inside the pump. Another cause of cavitation is air ingestion. Air ingestion can also cause damage to the pump of the washer. However, its consequences are less severe than vaporization.

● Water Overheating

The pressure washer pump builds pressure even when you are not spraying. When you stop squeezing the trigger, the pressure built by the pump does not relieve, and pressure continuously builds inside the pump. Unrelieved pressure does not damage the pump. This is because when you do not squeeze the trigger for some time, the unloader valve, also known as the thermal release valve, activates. The unloader valve diverts the water flow in a loop to the inlet. The pressurized water is depressurized in the bypass inlet and is again fed to the pump. This cycle continues until the water is released.

The unloader valve protects the pump with its bypass mechanism. However, you should not test its limits for too long. Overheating happens when the pump is in bypass mode for too long. When the same water is cycled through the pump, it gets warmer as the crankcase generates heat. If this water gets overheated, it can damage the pump of the pressure washer. Manufacturers allow up to 2 minutes for the water to cycle in bypass, but we recommend that you should not let your pressure washer run for more than 45 seconds without squeezing the nozzle. If you need to wait longer than that for some reason, you must turn off the washer and restart it when you are ready to use it.

The two most common reasons behind the pressure washer pump going bad are a faulty unloader valve and a clogged carburetor (in the case of gas-powered washers).

● Unloader valve

Many pressure washer problems start and end with the unloader valve. This important pressure washer component controls the pressure. It diverts the water flow into a loop to retain high pressure when the trigger is released. When you hear sputtering sounds coming from a gas pressure washer and the engine stalls, it means that the unloader valve of the washer has been damaged, probably due to an increase in the pump pressure.

The piston controls pressure retention and is one of the important parts of the unloader valve. The piston moves back and forth when the pressure washer is operating. When this movement is stopped or interrupted, the pressure washer stops. Remove the piston from the unloader valve and inspect it.

The pressure washer can also stop when the trigger is pulled due to worn-out or cracked O-rings. This can cause leakage at the pump and do not allow the unloader valve to work correctly. As a result, the pressure washer stops when the trigger is pulled. Check the O-rings of the unloader valve and replace them if they are cracked or damaged.

If the unloader valve is not working correctly, it can damage the pump. This happens when the unloader valve does not allow the water to divert in the loop to the inlet to release pressure. This builds up the pressure in the pump. When the piston takes longer to divert the flow of water, the pump is affected. Adjust the settings so that the unloader valve can divert the water back to the inlet to avoid pressure build-up that can damage the pump.

Is a pressure washer pump protector necessary?

In general, I recommend using a pump protector in cold weather and before storing your machine for an extended time. It is not necessary to use a pump protector after every cleaning job.

When the pressure washer is stored for an extended period, the water and moisture left inside the pump can cause corrosion, mineral deposits, and sticking of the valves. I recommend protecting the pressure washer pump in cold weather and for long-term storage. At temperatures below freezing, the water inside the pump will freeze and expand, damaging and even cracking the pump. A good solution is using a pump protector. The pump protector adds lubrication to the valves, pistons, and seals to prevent sticking.

Some manufacturers recommend applying a pump protector after every use. I do not think this is really needed. It is costly and does not give additional benefits. I recommend using a pump protector when you are going to store your equipment for the winter season.

● How to use a pump protector?

Use the following steps to use a pump saver/protector.

  • Step 1: Turn off the engine/motor
  • Step 2: Disconnect all the hoses.
  • Step 3: Open the bottle of the pump protector by unscrewing the top and removing the internal seal.
  • Step 4: After removing the seal, close the bottle again.
  • Step 5: Remove the protective cap at the top of the covering to expose the male garden hose thread.
  • Step 6: At the pump inlet, screw the pump protector bottle into the hose fitting.
  • Step 7: Inject the pump protector fluid into the pump by squeezing the bottle.   
  • Step 8: For gas-powered pressure washers, pull the starting cord until the pump protector fluid is released from the outlet. For electric pressure washers, simply turn on the pressure washer until the pump protector fluid is discharged from the outlet.
  • Step 9: Remove the protector fluid bottle from the hose fitting at the inlet.