We test the best Karcher pressure washer out on the filthiest patio

Instantly recognisable in that bright yellow and black, Karcher is one of the best-known brands in the business when it comes to pressure washing.

And you can pick a basic model up, the K 2 compact, for around £69. But what happens if you tick every box on the Karcher website and opt for the most expensive model on the list?

To save you looking, it's the K 7 Premium Smart Control Flex, and it's a remarkable thing. It costs £479.99 and it's so smart it even connects to an app.

Let me take you through some of the specs. It has 180 bar of pressure, a 550 litre per hour flow rate, a 10 metre hose, and a telescopic handle.

Its smart features include a Bluetooth connection to Karcher's Home and Garden app, and there's even a digital control panel on the lance handle that lets you configure the power output to suit different jobs.

After a mild and wet autumn and winter, my patio slabs were in dire need of a jetwash, so I got the K 7 out of the box and put it straight to work.

Setting up the control panel on the lance was quick and easy, it connected to the app very quickly, and the only other bit of preparation I needed to do was to connect the lance to the hose and screw on the garden-hose adaptor.

I flicked the switch and it leapt into life with an absurd amount of power. I nearly damaged my lawn, because I just wasn't quite ready for how strong the pressure from the jet would be.

Turning the power down a few notches is easy, there's a plus and minus button on the lance, but I turned it towards my slabs, twisted the chunky nozzle to the flat setting, and let rip.

I've used quite a few pressure washers on my patio over the years, but the K 7 is truly remarkable. It made light work of the baked-on algae because its pressure and flow rate is only slightly lower than the power you get from Karcher's Professional range.

This meant I was able to polish off my patio in record time and, when it came to cleaning off the surfaces that had been peppered in dirty water, I was able to turn down the power a bit and clean them off.

That's one of the best bits about the K 7, other than the huge power output - the digital control panel feels like a gimmick at first, but you quickly realise the value of being able to ease the pressure a bit.

Cleaning a bike, for example, isn't something you'd want to do at full power, neither is hosing down a piece of patio furniture, or a wooden fence. You'd literally peel the paint off.

The app, to be honest, probably is a bit of a gimmick. It's available on lots of the Karcher pressure washers, and gives you some handy setup instructions, and walks you through an assembly process if your pressure washer needs assembly (the K7 doesn't) but it then does little more than offer some tips for general outdoor jobs.

But I realise some people will value the way it walks you through the pairing of the smart control system, and it does give you quick access to the help centre if you have any issues.

The K 7 is compatible with Karcher's premium accessories, and I'm yet to test the surface cleaning tool on my driveway, or the "Plug and Clean" detergent system but, just as a straight forward pressure washer, it blew me away. Almost literally.

It's a very heavy thing, which is worth bearing in mind if you have to lug it up and down any steps regularly, but the suitcase-style telescopic handle is really useful, and the hose is a doddle to wind away on the built-in reel.

If you don't catch it on a special offer, as there is available at the moment, the recommended retail price is £599. And that's a lot of money for a garden tool.

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But at £479.99, it's good value for money, as long as you want the best domestic pressure washer on the market.

Is it worth buying it over the cheaper versions? It's hard to ignore the fact that a £69 K 2 Compact will do a pretty decent job, but if you want to clean a filthy patio, it'll take a lot longer and with 110 bar of pressure it won't hack away at the dirt as effectively.

And you won't get that superb control panel either. That really is a handy thing to have, especially for the lighter jobs you'll inevitably want to do to make the most of your investment.

And the K 7 Premium Smart Control Flex might be just that, but it's built to last, and it gets jobs done quickly. What more could you ask for?