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.

Vehicles

Paving and concrete

Around the house

Roof and gutters

Timber

Outdoor gear

What the machines actually deliver

Do not pressure wash these

• Fibro and asbestos cement sheeting on anything built before about 1990: roof sheets, eaves, wall cladding, fences, garage and shed walls

  High pressure water breaks down the cement matrix, throws asbestos fibres into the air and spreads contaminated debris across your yard and the neighbour's. Prohibited for anyone doing this as work anywhere in Australia: under the WHS Regulations (reg 446) a person must not use high pressure water spray or compressed air on asbestos or asbestos containing material, and it is prosecuted, with a Queensland painter fined for high pressure water cleaning an asbestos roof. In Western Australia it is prohibited outright, not just at work, under the Health (Asbestos) Regulations 1992. Outside WA the WHS ban bites on work rather than on an owner occupier personally, but the fibres and the bill do not care about that distinction: WorkSafe WA report clean up costs of between $7,000 and $50,000 on properties contaminated this way. Asbestos Victoria say it in one line, never use high pressure water cleaning methods, and Gerni print the same prohibition in their Australian manual.

  Instead: Assume any pre 1990 sheeting is asbestos until it is tested. If it has to be cleaned before painting, use non abrasive methods only: a cleaning solution applied and washed off with low pressure water, or wiping with a damp cloth, with the runoff captured. If the sheet is already cracked, chalky or broken, the answer is replacement by a licensed removalist, not cleaning. Ring your state regulator or council before you start.

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

  Gerni's Australian manual tells you to stand on a stable surface and to expect the gun to kick back when you pull the trigger, and the same manual range 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. Monier say walking on roofs can be dangerous and may result in injury, damage or a void warranty. Falls are the way this job puts people in hospital, not the water.

  Instead: Do it 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 overhead service line at gutter height: outdoor power points, light fittings, switchboards, meter boxes, solar inverters, pool pumps, extension lead joins and the machine itself

  Both Gerni and Karcher state the jet must not be directed at live electrical equipment or at the appliance. High pressure water 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. The one most people miss is overhead: on a lot of Australian houses the electricity service line lands on a bracket at the fascia, right at gutter height. Ausgrid's advice for gutter work is not to let any part of you or the guttering touch the wires or their connections, and a pressurised jet of water is a better path to earth than a length of gutter.

  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 the service line. Keep the jet, the lance and yourself well clear of it and of the meter box conduit, and if it runs through the work area ring your distributor before you start rather than after. Keep extension lead joins dry and off the ground, on a reel that holds the socket at least 60 mm clear, 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. Gerni put the thrust on the lance at up to 16.4 N in normal use and warn that high pressure injection injuries are medical emergencies needing immediate medical advice, because the entry wound looks trivial and the damage under it is not. The jet also flings grit and debris 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 kids 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 a P2 or FFP2 respirator for any mould job, any roof job, anything near old cement sheet and any dried droppings, and hearing protection if you have hired a petrol machine.

• Lead painted surfaces, meaning most Australian houses painted before about 1970

  WorkSafe Victoria class using a high pressure water jet to remove any surface coated with paint containing more than 1 per cent lead by dry weight as a regulated lead process. Blasting it spreads lead loaded paint chips and water across your soil, the neighbour's yard and wherever the kids and the dog play. Lead exposure is cumulative and there is no safe level for young children.

  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 with a tool that abrades and vacuums the water and debris at the same moment, and contain and dispose of the waste properly. For a whole house repaint, get a contractor who works lead safely.

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

  Gerni's Australian manual is explicit: this product must not be connected to the potable water mains without back flow prevention, and you must check local and national plumbing regulations before connecting. 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 bleach, wheel cleaner, degreaser or roof biocide drawn through the detergent injector. Gerni also note that water which has passed through a backflow preventer is no longer potable.

  Instead: Fit an approved backflow prevention device at the tap before you connect anything, and ask your water authority or a licensed plumber which type they require, because it varies by state and by what you are drawing. Once it is fitted, treat that tap and hose as non drinking water, and tell anyone else in the house the same.

• Dried bird, bat and possum droppings

  Blasting dried droppings does not remove a health hazard, it turns one into an aerosol you then breathe. WorkSafe Queensland's method for bird and bat droppings is the opposite of a pressure washer, and NSW Health note psittacosis is caught by inhaling bacteria from dried droppings and feather dust. This matters here more than most places: flying fox roosts over a deck or carport, corella and cockatoo flocks on a Colorbond roof or solar array, possums on a verandah rail.

  Instead: Mist the droppings with plain or soapy water and keep them wet the whole time you are removing them, then clean with water and detergent and apply a disinfectant. P2 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 down the street gutter or into a stormwater pit

  Stormwater is not connected to the sewer. It runs untreated to the nearest creek, and wash water carrying detergent, oil, brake dust and heavy metals is a pollution offence in most states. EPA Victoria fined a Northcote car wash operator $4,070 in February 2026 after bright green wash water reached a drain feeding Merri Creek, and SA EPA list vehicle washdown water among the pollutants that come off a suburban block.

  Instead: Wash the car on the lawn. On a driveway, work the water towards a garden bed or lawn and let it soak in. If the fall of the slab gives you no choice, block the pit with a sandbag or a drain mat while you work and clear it afterwards. Only rain belongs in a stormwater drain.

• Unsarked tile roofs, which is most Australian tile roofs laid before the 1990s

  With no sarking there is nothing between the tile lap and your ceiling. Water forced up under the laps runs down the battens into the ceiling cavity, and it rarely shows on the day. It turns up as ceiling stains, sagging plaster and soaked insulation the first time it rains properly. Monier strongly advise against pressure washers for roof cleaning because of the risk of tile damage, and blasting also strips the surface so the moss comes back faster and thicker.

  Instead: Check for sarking through the manhole first. If you can see the underside of the tiles, there is none. Either leave it alone or have it soft washed by a qualified roof cleaner who puts a moss and lichen treatment on at low pressure and lets the chemical do the work. Do not walk on the tiles yourself. If the roof feeds a rainwater tank, the downpipe or first flush diverter comes off before any treatment goes on.

• Soft, old or drummy render and texture coatings

  Dulux AcraTex set the limit for coated exterior walls at less than 450 psi, which is 31 bar. That is about a fifth of what a Karcher K 5 or a Gerni 7300 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. Dulux also say that under no circumstances should heavy staining be removed with a high pressure water blaster.

  Instead: Tap the wall first with your knuckles. Anything that sounds hollow, keep the machine off it completely. Wash with a fan jet of cold water under 450 psi, held at 45 degrees to the wall and at least 300 mm off it. For a patch of grime, put the machine down and use a scrubbing brush with detergent and warm water.

• 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.

  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. Filters every one to three months, a professional service once a year.

• PVC cafe blinds, canvas awnings and shade sails

  Coolaroo's own care advice for a shade sail is a garden hose rinse for dust and pollen, or mild soap and water for stubborn spots, and explicitly not a stiff brush, a scouring pad or an abrasive cleaner. Trade guidance goes no further than low pressure and a long standoff on HDPE shadecloth, and says no pressure washer at all on PVC, canvas and cover fabrics. A close jet blows the stitching out of a seam, tears a D ring corner and strips the UV coating, and it will end a 15 year fabric warranty. Most of the damage happens by accident, while someone is doing the pavers underneath.

  Instead: Hose, mild soap, soft brush, rinse, and let it dry before it goes back up. When you are washing the paving under a blind or sail, unclip it or drop it out of the way first rather than working around it.

What the nozzle colours mean

Setting up and packing away

• Backflow prevention, before you connect anything. Gerni state that the product must not be connected to the potable water mains without backflow prevention, and that you should check local and national plumbing regulations before connecting. A pressure drop on the main while you are working can pull the contents of the hose back towards the house supply, and on these jobs that could be bleach, wheel cleaner, degreaser or roof biocide drawn through the detergent injector. Fit an approved device at the tap, ask your water authority or a licensed plumber which type they require, and treat that tap as non drinking water afterwards, because Gerni note water that has passed through a backflow preventer is no longer potable.
• Electrical setup. The machine must run through a residual current device rated at 30 mA or less. An extension lead must be rated for outdoor use, kept dry and off the ground, ideally on a reel that holds the socket at least 60 mm clear, and fully unwound so it does not overheat. Gerni's maximum lead lengths are 12.5 m at 1.0 sq mm, 20 m at 1.5 sq mm and 30 m at 2.5 sq mm. A Gerni Super draws 9.0 A, so it wants a circuit that can carry it. Never direct the jet at live electrical equipment or at the machine itself, and never remove or bypass the 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. Both brands warn that inhaling the aerosol a pressure washer creates can be hazardous. Gerni's guidance is to use a shielded nozzle where you can, and where a shield is not practical, a respiratory mask of class FFP2 or higher depending on what you are cleaning. In practice that means a P2 or FFP2 respirator on any mould job, any roof job, anything near old cement sheet and any dried bird, bat or possum droppings. Add hearing protection if you have hired a petrol machine. Expect the gun to kick back when you pull the trigger.
• Both feet on the ground. Gerni's 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 from the spray 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. Monier add that walking on roofs can be dangerous and may cause injury, damage or void a warranty.
• Check the age of the house before the first trigger pull. Two things stop the job dead. Sheet cladding, eaves, fences or roof sheets on anything built before about 1990 may be asbestos cement, and using high pressure water on it is prohibited for anyone doing it as work anywhere in Australia under the WHS Regulations, prohibited outright in WA, and has cost owners between $7,000 and $50,000 to clean up. Paint on anything built or last painted before about 1970 is likely to contain lead, and WorkSafe Victoria class high pressure water jetting of paint over 1 per cent lead as a regulated lead process. Test before you wash, on both counts. Karcher's own operating instructions say it plainly as well: do not spray any objects which contain harmful substances such as asbestos.
• Water restrictions, which are stricter than most people expect for hard surfaces. Washing the car at home with a high pressure unit, a trigger nozzle hose or a bucket is generally fine at any time. Hosing a driveway is not. Victoria's Permanent Water Saving Rules say water must not be used to clean hard surfaces such as concrete, paths and driveways except after an accident, fire, health or safety hazard or emergency, or where staining has developed and then only once a season, or during construction or renovation, and then by means of a high pressure water cleaning device where one is available. Victoria defines a high pressure water cleaning device as one whose rate of delivery is 9 litres per minute or less, which puts a hired petrol unit and some high flow machines outside the definition. Greater Sydney's year round Water Wise Guidelines carry the same hard surface prohibition. Rules vary by state, authority and season, so check your own water authority before you start.
• Decide where the water goes before you turn the tap on. Stormwater is not connected to the sewer, it runs untreated to the nearest creek, and letting wash water carrying detergent, oil, brake dust or roof biocide reach a street gutter or a stormwater pit is a pollution offence in most states. EPA Victoria fined a car wash operator $4,070 in February 2026 after wash water reached a drain feeding Merri Creek. Wash vehicles on the lawn. On a slab, work the water towards a garden bed, and if the fall gives you no choice, block the pit with a sandbag or drain mat while you work.
• Noise and the neighbours. In NSW, under the Protection of the Environment Operations (Noise Control) Regulation 2017, power tool noise must not be audible in a neighbour's habitable room before 8 am or after 8 pm on Sundays and public holidays, or before 7 am or after 8 pm on any other day. Other states set their own prescribed hours through their EPA or environment department, so check yours rather than assuming. A hired petrol unit is loud enough that this becomes a real complaint, not a theoretical one, and it is loud enough that you should be wearing hearing protection yourself.
• 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. Gerni warn 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.

• ▸Inlet hose, minimum length. Karcher Australia 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. Gerni specify an ordinary half inch garden hose of at least 10 m and no more than 25 m.
• ▸Inlet hose, diameter and fittings. Gerni specify a reinforced garden hose of at least 12 mm internal diameter for the inlet on the 7300. Karcher say to avoid aquastop fittings because they restrict flow, and to use standard tap fittings. Gerni also warn against long thin hoses generally and say use at least half inch. 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.
• ▸Check your tap actually delivers enough. Karcher Australia's own test is the bucket test: time how long the tap takes to fill a known volume, work out the L/min, and compare it with the machine's rated flow on the model tag. A K 5 wants 8.3 L/min and a K 2 wants 6. If the tap cannot beat the machine's rated flow with the hose attached, it will pulse and fade no matter what else you do. This is also the reason most domestic machines cannot keep a surface cleaner fed at their headline flow.
• ▸Maximum inlet pressure. Gerni cap the inlet at 1 MPa, which is 10 bar or about 145 psi. That is above normal Australian mains pressure in most places, but a booster pump or a bore pressure system can beat it. If you are on a pump, check its cut out pressure before you connect the machine.
• ▸Maximum inlet temperature, and the suction mode trap. Karcher K 3 and K 4 are limited to 40 degrees C, the K 7 WCM allows 60. Gerni 5000, 5300, 5400, 7000 and 7300 all allow 40. The older Gerni Super range allows 60 on mains but only 20 degrees C when drawing from a tank or bucket in suction mode, and that 20 degree figure is the one that catches people out: a rainwater tank in a Queensland summer is over it. A black poly hose lying on a driveway in February is well over 40 on its own, so flush the hose to waste before you connect it.
• ▸Running off a rainwater tank or a bucket. Both brands allow it, and Karcher Australia publish it as the way to keep cleaning under restrictions, claiming up to 80 per cent less water than a garden hose. Gerni say 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 tank, 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. Karcher's SH 3 suction hose is 3 m, the machine should sit no more than 0.5 m above the water, and they say to bleed it on low pressure for up to two minutes with the lance off. Use a suction filter and never let the tank run dry mid job.
• ▸Water quality on tank and bore supply. Gerni say to use only water without impurities, and that where there is a risk of silt, sand or sediment, for example from your own bore, an additional filter should be fitted. Sand destroys pump valves and that damage is not a warranty claim. The machine's own inlet filter must always be fitted, and Gerni state that failure to fit it invalidates the guarantee. Separately, BlueScope warn against hard mineral rich bore water on Colorbond, which is standard supply across Perth and much of regional Australia and is exactly what causes the orange staining people are trying to wash off in the first place.
• ▸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 Vario Power or variable nozzle 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. Karcher note their machines are designed for Karcher detergents and that thicker non brand products may not draw and may affect warranty.
• ▸Detergent rule two: apply it right. Gerni's method is to put foam or detergent on so the chemical is in direct contact with the dirt, and to 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. If you are using bleach on mould, NSW Health's dilution is 250 mL of bleach in 4 litres of water, not the much stronger mixes you see quoted, and never mix bleach with vinegar, ammonia or an acid cleaner.
• ▸Detergent rule three: flush it afterwards. Gerni's maintenance instruction is to rinse the detergent spraying attachment after use, and to 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 and long term storage. Store the machine 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. Gerni state the machine must not be used below 0 degrees C, that you must never start a frozen machine, and that frost damage is not covered by the guarantee. This matters in Canberra, the Southern Highlands, the Victorian high country, Tasmania and anywhere inland that frosts, not just the snowfields.
• ▸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 Gerni say clean it immediately. Keep the cooling vents clear. Grease the couplings regularly so the O rings do not dry out, and clean dust and sand 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 160 bar machine at 6 L/min feels slower on a driveway than a 130 bar machine at 8.5 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 bar litres per minute, the one number that lets you compare two machines fairly. Karcher K 2 at 121 bar and 6 L/min is 726. Karcher K 5 at 159 bar and 8.3 L/min is 1320. Gerni 7300 at 160 bar and 8.3 L/min is 1328. So the K 5 and the 7300 are near enough twice the machine the K 2 is, even though the label pressure is only about a third higher. Some Australian suppliers divide that figure by 600 to give a small index, so 83 bar at 6 L/min scores 0.83 and the same pressure at 12 L/min scores 1.66. Bar litres per minute is also how AS/NZS 4233.1-1999 classifies high pressure equipment: Class A is more than 800 and less than 5600 and is a one person operation with no accredited training, Class B is above 5600 and needs two people and accredited training. Most domestic machines sit right at the bottom of Class A, and the smallest fall below it entirely: the K 2 at 726 and the Gerni 5000 on its rated figures at 609 are both under the 800 floor.
• ▸Hire or buy. Indicative hire from Bunnings is $69 for 24 hours on a 3000 psi petrol unit plus a $100 deposit, with 4 hour and 7 day tiers either side, and Kennards and similar yards go up from there to industrial petrol and trailer mounted diesel. Break even against a Karcher K 4 or K 5 is roughly two to three hires. The decision rule: hire a petrol machine for a one off large area of plain concrete where you genuinely want the pressure, buy an electric machine if you wash cars, bikes and furniture regularly, because that job is flow and detergent rather than pressure. Do not hire a big machine for a house wash, a deck or a Colorbond fence, because it is the wrong tool for all three and it comes with fixed colour tips instead of an adjustable lance. Prices move, so check before you book.

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.

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Symptom to fix

No pressure, or the pressure has dropped right off

Vario Power or variable nozzle still wound back on the low pressure detergent setting. Nozzle bore blocked with grit or lime. 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. Never run the machine with the filter out, Gerni say failure to fit it invalidates the guarantee. Uncoil the garden hose fully off any reel and open the tap all the way.

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. Gerni say to avoid long thin hoses and to use at least half inch, and specify a reinforced hose of at least 12 mm internal diameter on the 7300. Then clean the nozzle and the inlet filter. Do the bucket test at the tap and compare what it actually delivers with the machine's rated flow.

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

Not plugged in, or a dead outlet. Machine is waiting on the trigger, which is normal on Karcher and Gerni machines. Circuit fuse or 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 outlet and try it without the extension lead, which is Gerni's own first test. Check the breaker rating against the machine's draw, a Gerni Super pulls 9.0 A. Size the lead properly: Gerni allow a maximum of 12.5 m at 1.0 sq mm, 20 m at 1.5 sq mm and 30 m at 2.5 sq mm, and say to unwind any lead 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 an authorised agent. Never remove or bypass the RCD.

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 Gerni print for this exact symptom. Check the supply voltage matches the model tag. If it has been below zero overnight, do not force it. Gerni's instruction is never to start a frozen machine, and frost damage is not covered by warranty.

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 tank or bucket. 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 tank, 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. Karcher 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. Karcher say their machines are designed for Karcher detergents and that other products may be too thick to draw and can restrict 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 sand off the couplings before assembling, and grease them regularly so the O rings do not dry out, which is Gerni'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. Gerni list a worn or damaged gun O ring as a cause of the machine starting and stopping on its own. Replace the O ring. If it still weeps, the gun needs replacing, and Gerni's instruction is to go to an authorised repair agent 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 an agent. 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, common on tank and bore water. Incorrect mains voltage. If it stops dead and restarts a few minutes later, that is the thermal sensor. Gerni say 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. On tank or bore water fit an extra external filter, because silt and sand 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 power point 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. Gerni's rule 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, not just at smoko. 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. Tank 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 by an agent 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 tank keep an eye on the level.

I striped the driveway 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 slab 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 a T-Racer or a Patio Cleaner rather than swinging a lance. If the slab is coloured, stencilled or stamped, stop now and get advice, because taking it back to an even finish will take the colour coat with it.

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. If you have a Gerni 7300 with 12 m on the reel you already have more reach than most, and 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 shed 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 shed or a garage in a frost prone area. Water expands as it freezes and splits the pump head or the valve housing, and Gerni state that frost damage is not covered by the guarantee. It needs an agent. 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. This matters in Canberra, the Southern Highlands, the Victorian high country, Tasmania and anywhere inland that frosts, not just the snowfields.

Inlet filter blocked

Sand, silt, lime or rust in the supply, worst on tank, bore and older galvanised 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. Gerni say do this at least monthly, or more often with heavy use, and that 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 sand into the machine. On tank or bore 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. Karcher Australia 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. Gerni allow a half inch hose from 10 m to 25 m and specify a reinforced hose of at least 12 mm internal diameter on the 7300.

Hot water put through a cold water machine

Feeding from a hot tap or a mixed supply. Feeding from a black poly hose that has been lying in the sun, which in an Australian summer gets there on its own. Drawing from a tank in suction mode in hot weather. Check your machine's limit before you connect anything warm. Karcher K 3 and K 4 stop at 40 degrees C at the inlet, the K 7 WCM allows 60. Gerni 5000, 5300, 7000 and 7300 all allow 40. The older Gerni Super range allows 60 on mains but only 20 degrees C in suction mode from a tank or bucket, which is the one that catches people out. 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 Gerni recommend for clearing sand out of it.