Pressure Washer Settings

Full chart

Pressure by surface, in bar and psi

Working pressure, not the machine's maximum. Start wide and far away, then close in: you can always add pressure, but you cannot put timber fibres or render back.

Paving and drives

Around the house

Roof and gutters

Timber

Vehicles

Outdoor gear

What the machines actually deliver

Do not pressure wash these

• Asbestos cement: garage and outbuilding roofs, soffits, rainwater goods and flue pipes in properties built roughly 1950s to 1999

  High-pressure jetting destroys the weathered cement matrix and releases large quantities of fibres plus a contaminated slurry across the garden. HSE treats high-pressure jetting of asbestos cement as exceptional and specialist-only, and prosecutions have followed from jet-washing asbestos cement roofing. The UK ban on asbestos came in 1999, so anything older than that is suspect until proved otherwise.

  Instead: Assume any corrugated grey cement sheet on a pre-2000 garage is asbestos until it is tested. Soft wash it or leave it alone. HSE task guidance sheet a12, cleaning weathered asbestos cement roofing and cladding, covers the controlled method. If the sheet is already cracked or broken, the answer is a licensed removal, not a clean.

• Pre-1919 brickwork laid in lime mortar, and any handmade or historic brick

  High-pressure jetting has sandpapered historic buildings, destroying both the brick and the mortar. Handmade bricks carry a protective kiln-formed fire skin; strip it and the soft porous core absorbs water and spalls in the first hard frost. Lime mortar is a deliberately sacrificial layer that is meant to be repointed, not blasted out, and once it has gone the wall takes water straight into the core.

  Instead: Clean water, a hand-held low-pressure sprayer, sponges and soft-bristle brushes, and no metal brushes. SPAB and Historic England both take this line. If the wall is listed or in a conservation area, get advice before you clean it at all, because the wrong method is a consent issue as well as a damage one.

• Lead-painted surfaces: joinery, windows, doors and railings painted before about 1970

  Paint applied before 1970 may contain lead, and it is common on British pre-war and Victorian joinery. Pressure washing atomises lead-bearing paint and spreads contaminated water and flakes across soil and hard surfaces where children play. Lead exposure is cumulative and there is no safe level for young children. HSE's prohibition on high-speed dry sanding and burning-off of lead paint is explicit; the extension to pressure washing is ours by analogy, because the mechanism is the same and the run-off makes it worse.

  Instead: Test the paint first with a lead test kit. If it is positive, do not water-blast it, do not dry-sand it and do not use a heat gun. Use a chemical stripper, or a wet method that abrades and vacuums at the same moment, and contain and dispose of the waste properly. For a whole house, get a contractor who works lead-safely.

• Anything you can only reach from a ladder, or by standing on the roof

  The manufacturer's manual for this class of machine tells you to stand on a stable surface and to expect the gun to kick back when you pull the trigger, and puts the thrust on the lance at up to 16.4 N. A ladder is not a stable surface and a wet roof is worse. Falls are what put people in hospital on this job, not the water.

  Instead: Work from the ground with an extension lance, or pay someone. If the only way to reach it is a ladder or a roof, that is the signal to stop, not a problem to solve with a longer reach. Scoop gutter litter by hand from a properly footed ladder with the machine switched off and the gun on the ground, then wash from below.

• Electrical fittings and the incoming service: outdoor sockets, light fittings, consumer units, meter boxes, solar inverters, pond and pool pumps, extension lead joins and the machine itself

  Every pressure washer manual states that the jet must not be directed at live electrical equipment or at the appliance. High pressure gets past weather seals that were only ever designed to shed rain, and the result is a short, a tripped RCD, or a fitting that stays live and wet. On older British properties the service head, meter box and any overhead drop are outside and unprotected.

  Instead: Switch off and cover or tape anything electrical before you start, meter box and inverter included. Look up before the first trigger pull and find any overhead line. Keep extension lead joins dry and off the ground, fully unwound, and run the machine on a 30 mA RCD.

• People and pets, including washing mud off your own boots or off the dog

  A domestic machine at 130 to 160 bar will cut skin. The manual puts lance thrust at up to 16.4 N in normal use and warns that high pressure injection injuries are medical emergencies needing immediate advice, because the entry wound looks trivial and the damage under it is not. The jet also flings grit back at eye height.

  Instead: Never point the lance at anyone including yourself, and never use it to clean clothing or footwear on a person. Keep children and animals out of the area. Eye protection and enclosed shoes every time, both hands on the lance, trigger locked whenever the gun goes down. Add an FFP2 or better respirator for any mould job, any roof job, anything near old cement sheet and any dried droppings, and hearing protection on a hired petrol machine.

• Connecting the machine to the garden tap with no backflow prevention

  Under the Water Supply (Water Fittings) Regulations 1999 every hose union tap must be supplied through backflow protection rated at or above the highest fluid category downstream. A pressure drop on the main while you are working can siphon the contents of the hose back towards the house supply, and on the jobs on this page that could be biocide, wheel cleaner or degreaser drawn through the detergent injector.

  Instead: A hose used only for watering a garden or washing a private car is a fluid category 3 risk, which a double check valve protects. As soon as detergent is drawn through the machine, or it feeds from a butt or tank, you are into category 5, which check valves cannot protect at all: that needs a type AA or AB air gap, in practice a break tank. Treat the tap and hose as non-drinking water afterwards.

• Dried bird droppings and pigeon guano

  Blasting dried droppings does not remove a health hazard, it turns one into an aerosol you then breathe. Droppings dry hard on roofs, gutters, solar panels and window sills, and the organisms in them are inhaled with the dust rather than caught by touch.

  Instead: Mist the droppings with plain or soapy water and keep them wet the whole time you are removing them, then clean the surface with water and detergent and apply a disinfectant. FFP2 respirator, gloves and covered clothing. Only bring the machine out once the dry material is gone and the surface is wet, and keep it on low pressure.

• Wash water into a surface water drain, including the kerb gully outside the house

  UK drainage splits into surface water, which goes to a watercourse largely untreated, and foul, which goes to treatment. Run-off containing cleaning chemicals, detergents or emulsifiers must never enter a surface water drain: it pollutes the watercourse and disables oil separators. A highway drain is a surface water drain, so washing a drive into the kerb gully sends the run-off to a stream. Commercial washing run-off is trade effluent, and discharging it to sewer without consent carries a fine of up to £5,000 per offence in the magistrates' court, or an unlimited fine in the Crown Court.

  Instead: Wash onto grass, a border, a soakaway or a permeable surface wherever practicable, use a biodegradable detergent, and never let detergent run into the road gully. Degreasers and high-pressure cleaning should only be used where the area drains to foul sewer, ideally in a designated wash bay. Hydrocarbons such as paraffin and white spirit must in no circumstances reach a surface water drain.

• Up under tile laps, on any pitched roof

  A jet fired upslope goes under the covering and into the roof, and on an older British roof with no membrane there is nothing between the tile lap and the ceiling. It rarely shows on the day: it turns up as a stained ceiling, sagging plaster and soaked insulation the first time it rains properly. High pressure also strips the surface of concrete tiles, so the moss returns faster and thicker.

  Instead: Work downslope only, and better still, do not do it at all. If a roof is being cleaned it is soft washed by someone insured for it: a moss and lichen treatment applied at low pressure, left to work, and rinsed gently. Do not walk on the tiles yourself.

• Soft, old or drummy render, monocouche and pebbledash

  Professional render cleaners work at around 50 bar, and K-Rend's own maintenance guidance is to use clean water and a mild detergent with the washer set on fan application, not high power. That is a fraction of what a mid-range machine puts out. Above it the jet cuts the coating off the substrate, and where the render has already lost its key and gone drummy it comes off the wall in sheets. Monocouche is coloured all the way through and cannot be patched invisibly.

  Instead: Tap the wall with your knuckles first and keep the machine off anything that sounds hollow. Soft wash it: biocide on at low pressure, dwell, gentle rinse or leave it to weather. For a patch of grime, put the machine down and use a brush with detergent and warm water.

• Heat pump and air conditioner condenser fins on the outdoor unit

  Condenser fins are thin aluminium about a millimetre apart. A pressure washer flattens them on contact, which blocks airflow and permanently drops the efficiency of the unit, and it drives water into the fan motor, the control board and the terminals inside the cabinet. It is also live electrical equipment, which every pressure washer manual tells you never to spray. This matters more every year as air source heat pumps go in.

  Instead: Isolate the unit at the switch, brush the fins gently from the inside out with a soft brush or a fin comb, and rinse with a garden hose on low pressure if it needs it. Leave anything beyond that to the annual service.

What the nozzle colours mean

Setting up and packing away

• Hosepipe bans cover pressure washers, and they cover most of this page. Under the Water Use (Temporary Bans) Order 2010, a hosepipe is defined to include anything designed, adapted or used to serve the same purpose, which catches pressure washers, sprinklers and irrigation. Of the eleven prohibitable uses, five are pressure washer work: cleaning a private motor vehicle, cleaning walls or windows of domestic premises, cleaning paths or patios, cleaning other artificial outdoor surfaces (defined to include timber decking) and the garden watering ones. During a Temporary Use Ban, washing a drive, patio, path, render, uPVC or a private car with a pressure washer is prohibited, and the maximum fine is £1,000 on summary conviction. Exemptions that matter: water not from the mains, so a machine fed from a water butt or rainwater tank is legal during a ban; Blue Badge holders and qualifying Priority Services Register customers; work needed to protect human health and safety; and businesses providing cleaning as a service, so the jet-washing firm may work while you may not. Note the vocabulary: a Temporary Use Ban is the company-issued domestic restriction, while a Non-Essential Use Ban or Drought Direction is a separate, more severe instrument that restricts commercial use too.
• Backflow prevention, before you connect anything. The Water Supply (Water Fittings) Regulations 1999 require every hose union tap to be supplied through backflow protection rated at or above the highest fluid category downstream. A hose used solely for watering a domestic garden or washing a private vehicle is a fluid category 3 risk, which a double check valve protects, so a standard garden tap feeding a pressure washer with clean water needs one. Add chemicals and the category rises: fluid category 5 is the highest and cannot be protected by check valves at all, it requires a type AA or AB air gap. In practice, if detergent is being drawn through the machine, or the machine draws from a butt or tank, the correct arrangement is a break tank with an air gap, not a check valve. Pre-July 1999 combined Type HUK1 taps with an integral double check valve remain lawful, but outdoor check valves are prone to freezing and failure, so on replacement fit a plain hose union tap and put the double check valve inside the house where it is frost-protected.
• Electrical setup. A domestic pressure washer plugs into a 13 A BS 1363 socket at 230 V, which is a theoretical maximum of about 2,990 W, so a 2.5 kW machine is using most of it. BS 7671:2018+A2:2022 Regulation 411.3.3 requires additional protection by a 30 mA RCD for socket-outlets up to 32 A and for mobile equipment up to 32 A for use outdoors; the limited risk-assessment exception applies to certain socket scenarios, not to mobile equipment used outdoors. In practice every outdoor circuit needs 30 mA RCD protection. If the socket is not RCD-protected at the consumer unit, use a plug-in RCD adaptor. Use an outdoor-rated extension lead, keep the joins dry and off the ground, and unwind the reel fully so it does not overheat. Never direct the jet at live electrical equipment or at the machine itself, and never bypass an RCD because it keeps tripping.
• PPE, and the aerosol you cannot see. Eye protection and enclosed shoes every time, both hands on the lance, and the trigger locked whenever the gun goes down. The manuals warn that inhaling the aerosol a pressure washer creates can be hazardous, and that where a shielded nozzle is not practical you need a respiratory mask of class FFP2 or higher depending on what you are cleaning. In practice that means an FFP2 respirator on any mould or biocide job, any roof job, anything near old cement sheet and any dried droppings. Add hearing protection on a hired petrol machine. Expect the gun to kick back when you pull the trigger.
• Both feet on the ground. The manual tells you to stand on a stable surface and to expect the gun to kick back when engaged, and warns that the reactive force can move the gun and lance and make the operator slip or fall. The lance carries up to 16.4 N of thrust. A ladder is not a stable surface and a wet roof is worse. Do high work from the ground with an extension lance, or get a contractor in. This matters more in the UK than the pressure figures do, because roofline work, gutters and render are exactly the jobs people try to reach from a ladder.
• Check the age of the building before the first trigger pull. Two things stop the job dead. Cement sheet roofing, cladding, soffits, rainwater goods and flue pipes on anything built between roughly the 1950s and 1999 may be asbestos cement, and HSE treats high-pressure jetting of it as exceptional and specialist-only: prosecutions have followed. Paint on joinery, windows, doors and railings from before about 1970 may contain lead, which pressure washing atomises and spreads across the soil. And brickwork from before about 1919 is laid in lime mortar, which jetting destroys. Establish which of those you are standing in front of before you connect the hose.
• Decide where the water goes before you turn the tap on. UK drainage splits into surface water, which runs to a watercourse largely untreated, and foul, which goes to treatment. Run-off containing cleaning chemicals, detergents or emulsifiers must never enter a surface water drain, and the kerb gully outside the house is a surface water drain. Degreasers and high-pressure cleaning should only be used where the area drains to foul sewer, ideally in a designated wash bay, and hydrocarbons such as paraffin and white spirit must in no circumstances reach a surface water drain. Wash onto grass, a border or a soakaway where you can, use biodegradable detergent, and if the fall of the drive gives you no choice, block the gully with a drain mat while you work. Commercial washing run-off is trade effluent, and discharging it to sewer without consent carries a fine of up to £5,000 per offence in the magistrates' court or an unlimited fine in the Crown Court.
• Breaks during a job. If you are stopping for more than five minutes, switch the machine off at the switch, unplug it, shut the tap, pull the trigger to relieve the pressure, then lock the trigger. The manual warns that failing to do this may damage the pump or cause the machine to overheat and malfunction, and a pressurised gun left lying around is the one that goes off when someone picks it up. Leaving a machine idling in standby while you move something is how pumps die.

• ▸Forget the combi boiler, check the cold mains flow. A pressure washer takes a cold mains feed and never touches the boiler, so the boiler is irrelevant to it. What matters is the flow rate at the outside tap, and in a lot of British properties that is genuinely marginal: under 10 L/min is low, 10 to 15 L/min is acceptable but could be better, and above 15 L/min is good. Where the combi does come in is as a symptom, not a cause: a combi-served house commonly needs about 12 L/min of cold mains to perform, so a shower that goes cold when someone runs a tap tells you that you are in a low-flow property and the pressure washer will hit the same wall.
• ▸The bucket test, and what a washer actually needs. Run the cold outside tap fully open into a 10 litre bucket and time it: litres per minute equals 600 divided by the seconds to fill. The machine's rated flow is its maximum draw and the tap has to supply at least that, with a practical minimum of about 7 L/min for any useful machine. A Kärcher K7 at 9.2 L/min or an HSS petrol unit at 10.8 L/min needs a tap comfortably above 10 L/min, or the pump cavitates and starves. This is the test to do before you buy or hire, not after: hiring a bigger machine does not help if the tap cannot feed it. If your flow is low, the answer is a water butt or IBC and a suction kit, which also sidesteps hosepipe bans entirely.
• ▸Inlet hose, minimum length. Kärcher specify a minimum of 7.5 m of good, new, soft garden hose, fully uncoiled off any reel. A hose that is too short is the most common reason one blows off the inlet, because the pump is pulling against a rigid column of water. The Nilfisk manual specifies an ordinary half inch garden hose of at least 10 m and no more than 25 m.
• ▸Inlet hose, diameter and fittings. Use a reinforced garden hose of at least 12 mm internal diameter on a larger machine. Kärcher say to avoid aquastop fittings because they restrict flow, and to use standard tap fittings. If the machine pulses, going up a hose size often fixes it on its own, and if you are planning to run a surface cleaner this is the difference between one that works and one that stalls.
• ▸Maximum inlet pressure. The manual caps the inlet at 1 MPa, which is 10 bar or about 145 psi. UK mains pressure is comfortably below that almost everywhere, but a booster pump or a private borehole system can beat it. If you are on a pump, check its cut-out pressure before you connect the machine.
• ▸Maximum inlet temperature. Kärcher's K2 and K5 are limited to 40 °C and the K7 Comfort Premium allows 60 °C, and machines in the older Nilfisk-built range allow 60 °C on mains but only 20 °C when drawing from a butt or tank in suction mode. Over the limit the pump seals and valves distort and you lose pressure for good. A black hose lying on a drive in a July heatwave gets warmer than you would think, so flush it to waste before you connect it.
• ▸Running off a water butt or an IBC. This is the single most useful setup tip on the page for a British household, because it solves two problems at once: it is exempt from a hosepipe ban, and it gets round a low-flow outside tap. The suction hose must not be too long, about 5 m, and the tank must not sit lower than the machine. Fill the hose with water first, put the whole hose in the butt, crimp the end so it does not drain, connect, then uncrimp. Start with the lance and nozzle off and run until all the air has escaped; Kärcher say to bleed on low pressure for up to two minutes. Use a suction filter and never let the butt run dry mid job. Remember the regulations point: as soon as you are drawing from a tank, or drawing detergent, you are in fluid category 5 territory and the tank must be fed through an air gap, not a check valve.
• ▸Water quality on butt and borehole supply. Use only water without impurities, and where there is a risk of silt, grit or sediment fit an additional filter. Grit destroys pump valves and that damage is not a warranty claim. The machine's own inlet filter must always be fitted, and the manual makes that a condition of the guarantee. In hard water areas, limescale in the nozzle bore is a routine cause of lost pressure, so clean the nozzle more often than the manual suggests.
• ▸The long garden hose problem. Every extra metre of garden hose, every coil left on the reel, every kink and every restricting fitting costs you flow at the pump inlet, and flow is what does the cleaning. The symptom is a machine that pulses, or one that starts strong and fades. The fix is to uncoil it completely, shorten the run, go up a diameter and take off any aquastop or flow control fitting. A long thin hose on a coil is the single most common reason an owner thinks their machine is faulty when it is not.
• ▸Detergent rule one: it only works at low pressure. Detergent will not draw through a high pressure nozzle. Wind the adjustable lance to the detergent setting, fit the foam sprayer, or take the lance off altogether. If it is not drawing, the setting is almost always the reason, not the injector. Kärcher note their machines are designed for their own detergents and that thicker products may not draw and may affect warranty.
• ▸Detergent rule two: apply it right. Put the foam or detergent on so the chemical is in direct contact with the dirt, and work bottom to top, for example up a car body, so it does not run down and leave clean streaks. Let it work for several minutes but never let it dry on the surface, because that can damage what you are cleaning. Only use cleaning agents designed for pressure washers, because other chemicals can affect the safety and operation of the machine. Never mix a hypochlorite product with an acid cleaner, and never apply biocide in full sun or before rain.
• ▸Detergent rule three: flush it afterwards. Rinse the detergent attachment after use, and wash off the water hose, high pressure hose, spray lance and accessories before putting them away. Dried detergent in a foam sprayer or an injector line is the reason it will not draw next time.
• ▸Winter storage, which in the UK is the difference between a machine that lasts ten years and one that lasts three. Store it somewhere frost free. Before storing, empty the pump, hose and accessories: stop the machine, detach the water hose and the accessory, restart and hold the trigger until no more water comes through the gun, then stop, unplug and wind up the hose and cable. Dry the parts. The machine must not be used below 0 °C, you must never start a frozen machine, and frost damage is not covered by the guarantee. An unheated garage, shed or outhouse drops below zero most British winters, so an unheated store is not a frost-free store.
• ▸Routine maintenance that keeps it alive. Clean the water inlet filter at least once a month, or more often with heavy use. Clean the nozzles, using the cleaning needle only with the nozzle off the lance, then flush the nozzle backwards with water. A blocked nozzle raises pump pressure, so clear it immediately. Keep the cooling vents clear. Grease the couplings regularly so the O rings do not dry out, and clean grit off the connectors before assembling anything.
• ▸Flow does the cleaning, pressure does the lifting. Pressure, in bar, breaks the bond between the dirt and the surface. Flow, in L/min, carries the loosened dirt away and covers ground. At the same pressure, roughly double the flow is double the cleaning speed, which is why a 180 bar machine at 7 L/min feels slower on a drive than a 150 bar machine at 10 L/min, and why a surface cleaner starves on a small machine. Choosing between two washers at the same price, take the flow. Choosing a setting for a delicate surface, take the pressure down and leave the flow alone.
• ▸Cleaning units: bar multiplied by L/min. Multiply the pressure in bar by the flow in L/min and you get one number that lets you compare two machines fairly. A Kärcher K2 at 110 bar and 6.0 L/min is 660. A K5 at 145 bar and 8.3 L/min is 1,204. A K7 Comfort Premium at 180 bar and 9.2 L/min is 1,656. A Nilfisk P150.2-10 at 150 bar and 10.1 L/min is 1,515, so it is within a few per cent of the K7 while sitting 30 bar lower, which is the better place to be for most of the surfaces on this page. The individual multiplications are our arithmetic on the manufacturer figures in the machine table, not published numbers.
• ▸Hire or buy. HSS hire a 150 bar Honda-engined petrol unit at 10.8 L/min, and that is the machine to hire for a one-off large area of plain concrete where you genuinely want the pressure and can feed it. Buy an electric machine if you wash cars, bikes, bins and furniture regularly, because that work is flow and detergent rather than pressure. Do not hire a big petrol machine for render, uPVC, decking, a fence or an old brick wall: it is the wrong tool for all of them, and it comes with fixed colour tips instead of an adjustable lance, so you lose the one control that makes the bands on this page usable. Check the hire price and the deposit before you book, and check your tap can feed it.

Flow does the cleaning, pressure lifts the dirt. Two machines at the same bar will not clean at the same speed if one moves half the water, which is why the cleaning-units figure (bar multiplied by litres per minute) tells you more than the number on the box.

Best electric pressure washers in the UK →

Symptom to fix

No pressure, or the pressure has dropped right off

Adjustable lance still wound back on the low pressure detergent setting. Nozzle bore blocked with grit or limescale. Water inlet filter blocked. Tap not fully open, or the garden hose kinked, still coiled on a reel, or too narrow. Aquastop or flow restricting fitting on the inlet. Split or blown high pressure hose. Work through it in that order and it is nearly always solved in the first three. Check the lance setting first. Swap to a different lance or nozzle to rule the nozzle out, and clear the bore with the supplied cleaning needle, but only with the nozzle off the lance, then flush it backwards with water. Pull the inlet filter, rinse it, refit it, and never run the machine with the filter out: the manual makes fitting it a condition of the guarantee. Uncoil the garden hose fully off any reel and open the tap all the way. In hard water areas limescale in the nozzle is a far more common cause here than anywhere else.

Pulsing or surging while you are using it

Air in the inlet hose or the pump. Water supply cannot keep up with the machine. Nozzle partially blocked. Inlet filter blocked. Garden hose kinked or still on the reel. Hold the trigger open and let it run until the pressure settles, which purges the air. If it does not settle, open the tap further, check for kinks and go up a hose diameter: the manual specifies at least half inch, and a reinforced hose of at least 12 mm internal diameter on the larger machines. Then clean the nozzle and the inlet filter. Finally do the bucket test at the tap: 600 divided by the seconds to fill a 10 litre bucket gives you litres per minute, and if that is below the machine's rated flow, nothing else you do will fix the pulsing.

Motor will not start at all, or it trips the RCD or the circuit breaker

Not plugged in, or a dead socket. Machine is waiting on the trigger, which is normal on most machines. Circuit breaker too small for the current draw. Extension lead too long or too thin for the load. Water in the plug, the lead join or the machine. Damaged supply cord or a genuine insulation fault. Try another socket and try it without the extension lead, which is the manual's own first test. Check the breaker rating against the machine's draw: a 2.5 kW machine pulls close to 11 A, which is most of a 13 A plug fuse. Size the lead properly and unwind the reel fully so it does not overheat. If the RCD trips repeatedly, stop. That is the 30 mA device doing its job and it means current is leaking to earth. Dry everything, check the cord, and if it still trips take it to a repairer. Never remove or bypass the RCD, and never run an outdoor machine on a circuit that has none.

Motor hums or buzzes but will not turn over

Low supply voltage. Cold machine, or a pump that has sat unused and stiffened. Pump or hoses frozen. Pull the trigger on the gun, which unloads the pump and lets the motor start. That is the fix printed in the manual for this exact symptom. Check the supply voltage matches the model plate. If it has been below zero overnight, do not force it: never start a frozen machine, and frost damage is not covered by the guarantee.

Motor runs but no water comes out

Tap off or inlet hose not connected. Inlet filter blocked. Nozzle completely blocked. Pump, hoses or an accessory frozen. Air lock after connecting to a butt or tank. Connect and open the water, then clean the filter and the nozzle. If it is frozen, wait for it to thaw before switching on. Running off a water butt, the hose has to be full of water before you connect it: fill the hose, crimp the end so it does not drain, connect it, then run the machine with the lance and nozzle off until all the air has escaped. Kärcher say to bleed it on low pressure for up to two minutes with the lance off.

Detergent will not draw

Machine still on the high pressure setting. Detergent too thick. Detergent hose or pickup blocked with dried product. Wrong gun, or a non standard hose length. Detergent only draws at low pressure. Wind the lance to the detergent setting, fit the foam sprayer, or take the lance off entirely, and try again. Kärcher note their machines are designed for their own detergents and that thicker products may not draw and may affect the warranty. Clear a blocked detergent hose with hot water. Rinse the foam sprayer after every use, which is the step that stops the blockage forming in the first place.

Leaking at the lance joint or a hose connection

O ring perished, cut or missing on the garden hose fitting or the high pressure hose. Connection not fully seated or not tightened. Grit in the coupling face. Dry, ungreased coupling. Check the O ring on the garden hose fitting and on the high pressure hose and replace it if it is flattened or nicked. Tighten the inlet and high pressure connections. Wash dust and grit off the couplings before assembling, and grease them regularly so the O rings do not dry out, which is the manual's routine maintenance instruction.

Trigger gun leaking or weeping when you release the trigger

Worn or damaged O ring in the spray gun. Grit through the valve seat. Gun trigger assembly worn out. A worn or damaged gun O ring is a listed cause of a machine starting and stopping on its own. Replace the O ring. If it still weeps, the gun needs replacing, and the instruction is to go to an authorised repairer rather than keep running it. A weeping gun keeps cycling the pump, which is what kills the motor over time.

Machine keeps cycling on and off by itself while the trigger is closed

Spray gun O ring leaking. High pressure hose leaking. Pump leaking. A dripping fitting anywhere downstream of the pump. Failed unloader valve. Any drip downstream of the pump bleeds pressure, the pressure switch sees it and restarts the motor, and round it goes. Shut the tap and look for water under the machine, along the hose and at the gun. A leaking hose gets repaired or replaced. Water appearing underneath the machine means the pump needs servicing. If everything is dry and it still cycles, the unloader has failed and it needs a repairer. Do not leave a cycling machine running while you walk away: it is the fastest way to cook a pump.

Machine cuts out mid job, or pressure is fine at first then fades away

Thermal sensor has tripped on the motor. Water supply cannot sustain the machine's flow over a long session. Nozzle partially blocked, which raises pump pressure. Inlet filter slowly clogging with silt or scale. Incorrect mains voltage. If it stops dead and restarts a few minutes later, that is the thermal sensor: leave it five minutes to cool. The fade pattern is usually supply, not the machine: do the bucket test, uncoil the hose, go up a hose diameter and shorten the run. Then clean the nozzle and filter. If you are drawing from a butt or tank, fit an extra external filter, because silt and grit destroy pump valves.

The pump got hot and lost pressure after I left it idling with the trigger off

Machine left running in bypass while you moved a ladder, taped a socket or answered the phone. Trigger released but the machine never switched off. Total stop system faulty, so the motor keeps running with the gun closed. With the trigger released the pump circulates the same water round and round and it heats up fast. Minutes of that will distort the seals and valves and you lose pressure permanently. The rule in the manual is that if you are stopping for more than five minutes you switch the machine off at the switch, unplug it, shut the tap, pull the trigger to relieve the pressure, then lock the trigger. Get into the habit of switching it off every time you put the gun down. If the motor keeps running with the gun closed, that is a fault, not a feature.

I ran it dry, even briefly, and now it is noisy or weak

Started the machine before opening the tap. Water butt or bucket ran out mid job. Supply hose pinched or kinked while it was running. Tap closed with the machine still on. There is no home fix for this one. The pump is water lubricated, so seconds of running dry scores the seals and valves, and that damage is not a warranty claim. Stop using it and get it looked at before you make it worse. Prevention is the whole answer: open the tap and let water run through the gun before you hit the switch, and on a butt keep an eye on the level, because a 200 litre butt only holds about twenty minutes of washing at 9 L/min.

I striped the drive and the lap marks will not come out

Lance held at an uneven height or an uneven walking speed. Stopping or hovering with the trigger down. Overlapping passes by too little, so every second strip got two hits. Using a lance at all on a large slab instead of a surface cleaner. Be straight with yourself about this one: zebra striping is etched into the surface and you cannot buff it out, spot clean it or wait for it to weather off evenly. The only fix is to take the whole area down to the same finish, and the practical way to do that is with a surface cleaner, walking at a steady pace with about a third overlap on each pass. That is the strongest argument on this page for owning or hiring one rather than swinging a lance. On block paving, remember the whole area will then need re-sanding.

I added hose to the high pressure side and now it is weaker at the tip

High pressure hose extended beyond the length the machine is rated for. Joiner or coupling with a smaller bore than the hose. Mixing a heavier trade hose onto a domestic gun. Pressure drops along a high pressure hose, so every extra metre costs you at the nozzle. Use the length the manufacturer supplies, or their own listed extension, and do not chain joiners together. If you need to reach further, move the machine rather than the hose. The better answer to a long run is a longer garden hose on the inlet side, not a longer high pressure hose on the outlet.

It sat in the garage over winter and now the pump head is cracked or it leaks from the body

Water left in the pump, hose or accessories through a frost. Machine started while still frozen. Stored in an unheated garage, shed or outhouse. Water expands as it freezes and splits the pump head or the valve housing, and frost damage is not covered by the guarantee. It needs a repairer. For next winter: before you put it away, stop the machine, take the water hose and the accessory off, restart it and hold the trigger until no more water comes through the gun, then stop, unplug, drain the gun and hose and dry the parts. Store it somewhere frost free. An unheated British garage gets below zero most winters, so this is the single most common way a pressure washer dies here.

Inlet filter blocked

Grit, silt, limescale or rust in the supply, worst on butt, borehole and older iron mains. Not flushing the garden hose before connecting it. Never cleaning it, which is the usual reason. Take the filter out of the water inlet, loosen it carefully with pliers if it is tight, rinse it, check it is undamaged and refit it. Do this at least monthly, or more often with heavy use; the filter must always be fitted or the guarantee is void. Run water through the garden hose before connecting it so you do not push grit into the machine. On a butt or borehole supply, fit an extra inline filter upstream.

Garden hose keeps blowing off the inlet

Garden hose too short, so the pump pulls against a hard column of water. Aquastop or flow restricting tap fitting on the inlet. Worn or perished quick connect fitting. Kärcher specify a minimum of 7.5 m of good, new, soft garden hose fully uncoiled off any reel, and say not to use aquastop fittings because they restrict flow. Use standard tap fittings. Replace anything old, hard or split. The Nilfisk manual allows a half inch hose from 10 m to 25 m and specifies a reinforced hose of at least 12 mm internal diameter on the larger machines.

Hot water put through a cold water machine

Feeding from a hot tap or a mixed supply. Feeding from a black hose that has been lying in the sun. Drawing from a butt in suction mode in hot weather. Check your machine's limit before you connect anything warm. A Kärcher K2 and K5 stop at 40 °C at the inlet and the K7 Comfort Premium allows 60 °C. Over the limit the pump seals and valves distort and you lose pressure for good. Flush the garden hose to waste before connecting it if it has been sitting in the sun, which is the same step that clears grit out of it.