In the end, I abandoned the brushes in favour of the vario nozzle, twisting it to the high-powered pencil jet spray (it also offers a wider, gentler spray). The impact was immediate, and within moments all the ingrained mud, oil and bird poo was nowhere to be seen. While all of the models can be used with detergent (the 1,300W model requires an external detergent pump), none come with any in the box. Pressure washer pump fails - Store the pressure washer in a frost-free place, such as a cupboard in the house, and make sure that the water is turned on and at adequate pressure before running the pump. Takes steps to remedy a pulsing pressure washer. For the money, the Mac Allister 1,800W is undeniably a powerful machine. Having also tried out the more-expensive Kärcher K4 Full Control, I’d say the two machines blast away dirt with similar gusto. In terms of brand loyalty and how many people bought the same brand of pressure washer again, an impressive 73% of Karcher owners (sample size: 329) said they had versus 10% of Nilfisk owners (sample size: 52).

Patio cleaner attachment: circular plastic hoods with a brush around the bottom edge. Stops you having to stoop and helps ensure dirty water doesn't spray everywhere. To be fair, that problem isn’t exclusive to this particular pressure washer, but at least with the Mac Allister 2,100W you get a built-in cable winder to help keep things tidy. Fewer owners of Karcher pressure washers experienced faults within the first seven years of owning it - 8% said they had (sample size: 2,271) versus 16% of Nilfisk owners (sample size: 185).For fences, dirty cars and cleaning grime off paving slabs, look for a model with 120 bars of pressure. Anything above this is best reserved for complete garden overhauls and other industrial outdoor tasks. Flow rate Variable fan-jet: also called variable pressure lances, these allow you to vary the force of the jet from a focused point to a broad fan. Medium duty pressure washers tend to be a mix of high-end own-brand models and cheaper premium-brand models. As such, you'll find a confusing array of high-powered-but-basic models by garden machinery brands such as Stihl or Nilfisk, mid-powered Karcher, Bosch or Vax models with some choice of accessories, and high-powered and highly accessorised machines from Qualcast and Mac Allister. Karcher were the first to introduce smart technology to pressure washers so you can connect them to your smartphone via an app. If you’ve ever tried to take on a muddy patio with just a brush and some elbow grease, you’ll know that some garden jobs just need a little extra investment.

As a result, I left the patio roof looking like an unfinished job. Again, that’s not a problem that’s exclusive to the Mac Allister 1,800W, but if you’re looking to buy a pressure washer for the purpose of cleaning your conservatory roof, you might want to reconsider. Mac Allister 1,800W review: Verdict Best for: Cleaning extensive areas of paving, grimy 4-wheel drive vehicles, commercial vehicles and caravans My other main gripe with this Mac Allister pressure washer is that the adapter that connects the water hose to the machine shattered the first time I turned on the tap. It’s possible I hadn’t connected it properly, but you’d still hope it would be more robust than that. Nilfisk's entry level models tend to have more powerful motors and come with an aluminium pump head rather than a plastic one for durability. Detergent tank: we found built-in but removable detergent tanks more convenient than bottle attachments in our tests.Having recently cleaned my patio while testing the Kärcher K4 Full Control, I decided to put the Mac Allister through its paces by cleaning my car, my wheelie bin and my conservatory roof. Karcher has a higher customer score of 78% (sample size: 2,271) versus Nilfisk's 74% (sample size: 185). This reflects how satisfied respondents are with the brand and how likely they would be to recommend it. The shorter hose and low power can make cleaning slow and difficult, and the motors tend to be noisy. The parts also tend to be flimsy and prone to frost damage. Medium duty

Pressure gauge: some more expensive models have a pressure gauge on the lance handle but, as the pump pressure doesn't vary, they're of little practical use. Buying a new pressure washer can be confusing. There are usually several models in each manufacturer's range, with different types of motors and impenetrable model numbers which mean that useful accessories are either included in the price, or have to be bought as an extra. Unlike your standard garden hose, pressure washers deliver serious power. They use a strong, concentrated jet of water to obliterate dirt in no time.Additional handles: some machines have a variety of handles that will make carrying it around while cleaning much easier. Basic machines come with one lance – a long tube with a nozzle at the end. A fixed lance can’t be adjusted, though you can move it nearer or further away from the area you’re trying to clean. You can also buy models with a variable pressure lance, where you can twist the nozzle at the end to alter the power of the spray – rather like a hosepipe attachment. This lets you create either a powerful narrow jet of water or a gentler, broad spray.

Hoses lengths vary from three metres, which is too short to wash a car; to five metres, which is an adequate length for car cleaning. Some of the cheaper pressure washers come with fixed nozzles that don't allow you to vary the water pressure.

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Our in-house experts at the GHI assessed the pressure washers' performance on common outdoor cleaning tasks, using their high-power jet sprays to take on muddy patios, windows and cars. The testers noted how easy the pressure washer was to set up, use, manoeuvre and, of course, the time it took to get the job done. Wheels: handy for heavier models. But, if you have lots of uneven ground or steps make sure you can still carry the machine.