Pressure Washer Not Building Pressure? 7 Common Faults and How to Fix Them

You pull the trigger, and nothing happens. Or worse, a pathetic trickle dribbles out where a powerful jet should be.

Your machine is running. The motor sounds fine. But the pressure has vanished.

This is the single most common fault we see at our Leighton Buzzard workshop. Nine times out of ten, the fix is simple. Sometimes you can sort it yourself in five minutes.

Here are the seven faults behind almost every pressure loss problem, and how to fix them before you spend money you do not need to spend.

Fault 1: A Blocked or Dirty Nozzle

This is the number one culprit. A tiny piece of grit lodges in the nozzle and chokes the water flow.

The machine still runs. The pump still works. But the pressure has nowhere to go.

Remove the lance and inspect the nozzle tip. Use the small cleaning pin that came with your machine, or a thin piece of wire. Push it through the nozzle from front to back.

Flush the lance with clean water and refit. If the pressure returns, you have saved yourself a service call.

Replace worn nozzles every six to twelve months on heavy use. A £15 nozzle can save hundreds in pump damage down the line.

Fault 2: Air Trapped in the Pump

Air in the pump is the second most common cause of weak pressure. It usually happens after the machine has been moved, stored, or had its water supply interrupted.

The pump cannot compress air the way it compresses water. So, pressure drops to almost nothing.

Run the machine with the trigger held open and the lance disconnected for 30 seconds. Let the water flow freely to purge the air out.

Reconnect the lance and test. In most cases, the pressure will come straight back.

If air keeps getting in, check your inlet hose for tiny leaks or loose connections. Air can sneak in through the smallest gap.

Fault 3: A Restricted Water Supply

Your pump needs a proper flow of water to build pressure. Starve it of water, and it starves you of pressure.

Check that your tap is fully open. A half-turned tap is a common mistake. Next, check the inlet filter on the machine. These clog with grit and limescale over time.

Remove the filter, rinse it under clean water, and refit. Do this every month if you work with hard water or dirty sources.

Also, check your garden hose. A narrow or kinked hose chokes flow before water even reaches the pump. Use a proper inlet hose rated for pressure washer use.

If your supply pressure is low, consider fitting a header tank to feed the machine with gravity-fed water.

Fault 4: Worn Pump Seals

Seals wear out. It is not a matter of if, only when.

When pump seals go, water leaks internally instead of being compressed. You get a weak, pulsing output that never quite reaches full pressure.

Signs to look for include water dripping from the base of the pump, a knocking or rattling noise during operation, and pressure that fades during use.

This is not a DIY job on most professional machines. Pump seal kits need to be fitted correctly, with the right tools and torque settings.

A professional seal rebuild usually costs around £150 to £250 and restores the pump to near-new performance. Far cheaper than a new pump or machine.

Fault 5: A Faulty Unloader Valve

The unloader valve controls pressure flow when you release the trigger. When it fails, pressure output becomes unreliable or vanishes completely.

Symptoms include pressure that builds then drops, the machine cycling on and off rapidly, or water spraying from the unloader housing.

On most Kranzle and Ehrle machines, the unloader is a serviceable part. A skilled engineer can strip, clean, and rebuild it in under an hour.

If your machine cycles on and off under load, do not keep using it. The repeated pressure spikes will damage the pump.

Get the unloader checked as soon as the symptoms appear. Ignoring it turns a small repair into a big one.

Fault 6: A Damaged or Leaking Hose

High pressure hoses take a beating. They get dragged over concrete, run over by vehicles, and kinked into tight corners.

A small leak or pinhole in the hose drops your pressure at the lance. You might not even see the leak at first. Check for a fine mist or wet patch along the hose length while the machine runs.

Replace damaged hoses immediately. A blown hose at 150 bar is dangerous and can cause serious injury.

Buy a genuine replacement rated for your machine's pressure. Cheap hoses fail fast and risk your safety.

Store your hose in loose coils, never tight bends. Hang it up rather than leaving it on the floor. A good hose will last years if you treat it well.

Fault 7: A Worn Pump Head or Valves

This is the big one. Worn valves or a scored pump head will kill your pressure permanently.

It happens from long-term neglect. Skipped services, dirty water, running the machine dry, or using it well past the warning signs.

You will notice a gradual loss of pressure over weeks or months. No single dramatic failure, just a slow decline.

At this stage, the repair is either a full pump rebuild or a pump replacement. On a premium machine like a Kranzle, a rebuild is often worth doing. On a tired cheap machine, a new washer makes more sense.

This is why regular servicing matters. A £90 annual service catches wear before it destroys the pump.

Frequently Asked Questions

Why does my pressure washer pulse or surge?

Pulsing usually means air in the pump, a blocked nozzle, or a failing unloader valve. Start with the simple fixes first before assuming the worst.

Can I fix a pressure washer myself?

Simple jobs like cleaning nozzles, rinsing filters, and purging air are easy DIY fixes. Anything involving the pump, unloader, or internal seals should go to a qualified engineer.

How often should a pressure washer be serviced?

Once a year for commercial use, or every 200 operating hours, whichever comes first. Heavy daily users should service twice a year.

What happens if I run my pressure washer dry?

Running dry for even a few seconds can destroy pump seals and valves. Always check your water supply before starting the machine.

How much does a pressure washer repair cost?

Simple repairs like nozzles and filters cost under £20. Seal rebuilds are £150 to £250. Major pump work is £300 to £600. A good service picks up problems before they get expensive.

Stop Guessing, Start Fixing

Most pressure loss problems come down to one of these seven faults. Work through them in order before assuming the machine is dead.

A five-minute nozzle clean or filter rinse fixes most issues. An annual service catches the rest before they become costly.

If you have tried the basics and the pressure is still weak, do not keep running the machine. Every minute of use under load makes the damage worse.

At RealKleen we have repaired every fault on this list thousands of times. Our workshop offers a 24-hour diagnosis on any drop-off, with fast turnaround on parts. Call Rob on 01525 370795, or drop your machine at our Leighton Buzzard base.

Get it fixed properly, once. Then get back to earning.