I’ve been testing the Kärcher K4 WCM Flex eco!Booster – it’s a great pressure washer for most people
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Powerful cleaning -
Duo of lances covers most bases -
Easy to use and store
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High-pressure hose can get messy -
No way to vary pressure
Kärcher’s K4 models are a step up from the basic K2 and K3 ranges, with more powerful water-cooled motors that deliver more pressure and are built to handle heavier workloads. We’ve often found them sitting near the sweet spot in the range; they’ll happily handle washing big vehicles and tackling jobs around the average-sized garden, but they’re not as big, heavy or expensive as the flagship K5 and K7 lines.
All of the above holds for the new K4 WCM Flex eco!Booster, but it also brings something new to the table. Like the K3 eco!Booster I looked at recently, the K4 comes with two spray lances. The first is Kärcher’s Dirt Blaster lance; great for scouring mud and caked-on dirt away with a fearsome rotary jet. The second is the new eco!Booster lance, which delivers a lower-pressure flat jet that still shakes off grime, but uses less water.
Is it worth checking out if you’re buying your first pressure washer or upgrading your existing Karcher model? I’ve been power-washing my garden and driveway with the K4 WCM Flex eco!Booster to find out where it excels, and pinpoint areas where it needs work.
What do you get for the money?
The K4 WCM Flex eco!Booster is a mid-range, mid-sized pressure washer capable of dishing out 20 to 130 bar of pressure and a maximum flow rate of 420 litres per hour. That’s 10 bar and 40 litres more per hour than the K3 eco!Booster, and that difference plays out in the price: the K4 WCM costs £250, £90 more than the K3 model.
The K4 also features a water-cooled, filtered pump, and the fittings for the high-pressure hose are brass rather than plastic, which should improve long-term reliability. I also found that the 8m of high-pressure hose provided was tougher than the 6m provided with the K3 model.
The K4 also gives you a bit more in terms of hose and cable management. You get chunky plastic hooks to store the hose and cable, as well as clips to store the spray gun and two lances. The Dirt Blaster lance handles more intense cleaning tasks, while the eco!Booster lance fires a wider, flat jet of water that’s easier on soft or damaged surfaces. I’d be nervous about using the Dirt Blaster on soft stone or areas of old tarmac; the eco!Booster is more gentle and cleans a wider area with each sweep.
The K4 takes more assembly than the K3, thanks to all those hooks and clips, but I still had it put together within 10 minutes. A cordless screwdriver can help you get the job done faster.
How easy is it to use?
Having used the K3 eco!Booster a few days prior, I immediately noticed the extra size and weight of the K4 WCM Flex. The main unit weighs a hefty 11.8kg, though with the thick plastic wheels and high carrying handle, it’s still not a huge effort to drag it around. The longer hose length and 5m power cable also help you get the water jet where it needs to go. The hose isn’t hideously prone to kinking – a common pressure-washer problem – and you can get around a car or garden terrace without constantly moving the pressure washer.
The two lances push into the spray gun’s nozzle and then twist to lock. The mechanism works pretty smoothly; you just need to ensure you don’t put in the eco!Booster lance upside down, as this may cause issues. Beyond that, there’s little to think about. There are no variable pressure levels or any settings to consider. You connect it to a mains extension and your hosepipe via the standard hoselock connector, turn it on, then pull the trigger.
How I tested the Kärcher K4 WCM Flex eco!Booster
I follow the same basic process when testing all pressure washers to compare ease of use and performance. I assemble the pressure washer according to the manufacturer’s instructions, then use it in a range of tasks around my home and garden, cleaning areas of tarmac, paving, plastic and timber. That way, I can see how well it handles walls, driveways, paths, patios and decking. I’ll also clean my car, paying special attention to the pressure washer’s ability to remove dirt and debris around the bodywork and wheels.
While doing all this, I’ll use any accessories provided, including foam spray bottles, additional nozzles, driveway brushes and car kits, to see if they make the job easier. Where the pressure washer claims any water-saving features, I’ll run tests spraying into a bucket for 30 seconds, then measuring the contents.
How well does it clean?
With more flow and pressure to play with than the K3 eco!Booster, there’s not much this sturdy pressure washer can’t do. I set it to work cleaning paving in my front garden, then blasting moss and debris build-ups from my driveway, and it did a stellar job on both accounts. The eco!Booster lance was particularly useful on the paving, enabling me to clean slabs with two or three sweeps that would have taken a lot more time and effort with a conventional jet. What’s more, I didn’t need to worry about damaging the stonework.
Having the dirt blaster lance so accessible makes it easy to switch if there’s anything you don’t think the eco!Booster lance can handle. I had some areas of paving where the local seagulls had cheerfully left their mark, and their droppings had dried to a consistency where the eco!Booster lance couldn’t shift them. For the dirt blaster lance, it was no problem, though I used it with some care to make sure I wasn’t damaging the surface.
An effective tag team of cleaning lances
Overall, the two lances form an effective tag team. I was clearing some dust and baked-on grime from the bottom of my car and its alloy wheels, and found I could clear large areas with the eco!Booster lance, then get into the wheels with the dirt blaster to clean off all the nasty residue. I found that the softer lance also works well on old decking, which can be wrecked if you’re heavy-handed with a high-pressure jet. After a while, swapping lances becomes second nature.
I was also interested to see whether the eco!Booster lance actually saved any water. Well, as with the K3 eco!Booster, there is a difference even if it isn’t massive. Spraying into a bucket with the dirt blaster lance, I filled it up by roughly 3.1 litres. With the eco!Booster lance that went down to 2.7l; a drop of just under 13%.
What could be improved?
Not a whole lot. It’s great to see brass connectors on the spray gun and high-pressure hose, especially if you regularly disconnect the hose for storage. However, it’s a shame that the hozelock connector for your hosepipe is just plastic. I also found it a bit tricky to store the high-pressure hose neatly after use. Even hung on the hook at the front of the washer, it tended to spring out in all directions unless secured with cable ties or something similar.
There might also be times, depending on what you’re doing, when you want something that comes in between the Dirt Blaster and eco!Booster lances in terms of force. For instance, you might want to clean areas of a bike or car without whacking them with the fierce jet of the first blaster, while I had some recently fitted paving that I was a bit nervous about exposing to the more brutal rotary jet. If you worry about these things, it might be worth considering a pressure washer like the Kärcher K4 Power Control or the Nilfisk Core 130 Bike & Auto, which have a variable lance and pressure settings.
Should you buy the Kärcher K4 WCM Flex eco!Booster?
This is going to be a great pressure washer for most people. It has the power to handle tougher jobs, but also the eco!Booster lance to make short work of larger areas of decking, driveway or paving. It’s very easy to use, reasonably easy to store and not too difficult to move around.
If you’re dealing with a lot of different surfaces and vehicles, you might want something with more settings or a variable lance, but the Kärcher K4 WCM Flex eco!Booster can save you water, time and backache.
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