Why Your Pressure Washer Is Losing Pressure

Nine times out of ten, a pressure washer that has gone weak is starving for water rather than dying of old age. Restricted inlet flow, a worn or wrong nozzle, trapped air or a clogged filter will all sap performance long before the pump itself gives up. Work through the water path from tap to nozzle and you will usually find the fault in a few minutes.

Start with the water going in, not the pump

A pressure washer pump can only push out what it is fed. If the inlet supply drops below what the pump is rated to draw, you get low pressure, pulsing, or a motor that cycles on and off. Before you touch anything else, run the garden hose into a bucket for a timed thirty seconds and see how much you collect. Multiply by two to get litres per minute. Most domestic machines want somewhere around eight to twelve litres per minute at the inlet, and the figure for yours is in the manual or on the spec plate.

Things that quietly choke the supply:

• The tap is only half open, or a shared outdoor tap is feeding something else at the same time.
• A long, narrow or kinked hose. A 15mm hose on a 25 metre run behaves very differently from a short 19mm one.
• A hose reel that has never been fully unwound, so the water is doing several tight turns under load.
• A cheap quick connector with a narrow bore acting as a restriction.
• Drawing from a water butt without a suction kit designed for it.

Check the inlet filter

Almost every machine has a small mesh or gauze filter where the hose screws into the body. It exists to stop grit reaching the pump valves, and it does its job by getting dirty. On mains water it can take a couple of seasons to block; if you have ever drawn from a butt or a jerrycan, it can happen in one afternoon.

Unscrew the inlet fitting, pull the filter out with pliers or a small hook, and hold it up to the light. If you cannot see clearly through the mesh it is restricting flow. Rinse it under a tap, brush it gently with an old toothbrush, and if it is torn or crushed, replace it. They cost very little and are model specific, so quote the machine number when ordering.

The nozzle is the usual culprit

Pressure at the surface is created by the orifice at the tip. As that orifice wears it gets larger, the same volume of water passes through more easily, and the pressure reading falls. Worn nozzles are gradual, which is why people blame the pump: the machine did not fail overnight, it faded across a season of patio work.

Two quick checks. First, fit a different nozzle. If pressure returns, the original is worn or partially blocked. Second, look at the spray pattern from the side. A healthy fan is a crisp, even sheet. A worn one is ragged, fuzzy at the edges, or noticeably wider than it used to be.

Blockages are just as common. A single grain of sand sitting in the orifice will kill performance. Clear it with the pricker wire that came with the machine or a fine needle, working from the front, then flush water backwards through the nozzle to push debris out the way it came in. Never poke it with anything harder than the tip material, because scoring the orifice ruins it permanently.

Look for leaks under load

Water escaping between the pump and the nozzle is pressure that never reaches your patio. With the machine running and the trigger held, walk the whole hose and look for spray, drips or a weeping collar. Common spots are the high pressure hose connection at the machine, the connection at the gun, and the O rings inside quick release couplers.

O rings are consumables. They flatten, harden and split, and a set costs a couple of pounds. If a joint leaks only under pressure and looks dry at rest, that is almost always the O ring rather than the fitting.

Trigger gun and lance

An old trigger gun can leak internally without showing anything outside. If pressure is fine at the machine outlet but poor at the lance, and the hose is sound, the gun is a strong suspect. They are usually cheaper to replace than to rebuild.

Air in the system

Trapped air shows up as pressure that surges and drops rather than a steady weak flow. Turn the machine off, open the tap fully, and hold the trigger open for thirty seconds or so until the water runs without spitting. Then start the motor. If the pulsing continues, you have an air leak on the suction side, most often a loose inlet connection or a perished washer in the hose fitting.

When it really is the pump

If the supply is good, the filter is clean, a brand new nozzle makes no difference and nothing is leaking, then the pump has lost its ability to seal. Worn valves or seals are the usual cause, and heat, running dry, and frost damage are what get them there. On a mid range domestic machine a rebuild kit is often uneconomic once you factor in labour, though pumps on better built units are frequently sold as a serviceable part.

Frost is worth calling out separately. Water left in the pump over winter expands as it freezes and cracks internal components. The machine may still run and still push some water, but it will never hold full pressure again. Draining before the first cold snap takes five minutes and prevents an expensive lesson.

A sensible order to work through

1. Measure the actual flow at the tap with a bucket and a watch.
2. Fully unwind the hose, remove kinks, open the tap all the way.
3. Pull and clean the inlet filter.
4. Purge air with the motor off and the trigger held open.
5. Swap in a different nozzle, or clean the existing one.
6. Run the machine and inspect every joint for leaks under pressure.
7. Only then start suspecting the pump.

Following that order matters, because fixing a starved inlet after you have already ordered a pump rebuild kit is an annoying way to learn the lesson.