Top critical review
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Good piece of kit with some limitations
on 23 February 2015
Feb 2015: This certainly cleans the back patio well. Both the vario-lance and the surface cleaner are useful in removing the layer of algae that has accumulated. However, I have significant reservations:
Although the K4 works well on the patio, which has stone flags, sealed with cement, it's less satisfactory on the block driveway, where it creates a mess washing out all the sand that I spent hours brushing into the cracks.
It is easily pulled over by the two coils of tubing (the suction tube and the one that delivers the pressurised water). The detergent casing is now cracked as a result of one fall.
I could not break the seal on the detergent bottle just by inverting it on the plastic spike. In the end my Swiss Army knife did the trick and got it working. It seems to have stopped delivering detergent again, even though the bottle is still almost full.
The suction hose arrived separately as a piece of tightly-coiled tubing and this is the biggest problem. I have not been able to uncoil it, so it's effective length is between a third and a half of its real length. I've tried stretching it out in the garage for a few days but it still coils persistently. This means that it coils back on itself in my water butt and then sucks in air. The clip that is supposed to retain it in the water butt is useless and it all too easily pops out, smashing the filter (which is now broken) on the patio. Someone has suggested weighting it down with metal weights (is this part of your design, Kärcher?). I've tried fixing it to a piece of plastic tubing that I had around, but this is not heavy enough.
The other problem is filling it with water to prime it. Again, due to the way it coils on itself, this is difficult and certainly a recipe for ice-cold fingers in the winter. To be honest, you only need to have it partly filled with water. I've considered buying a much longer piece to help me reach the bottom of my drive but the thought of priming a longer tube puts me off. I don't want to run the K4 off the mains tap for environmental reasons.
Anyway, between trying to stretch the tubing sufficiently to use it without it popping out of the water butt and stop it coil itself so the filter is out of the water, it's a fairly useless piece of over-priced tubing. I'm thinking of rigging up a compromise that will run off the tap on the water butt with a filter in the tubing. I'll have to find an adapter as the water butt tap is quite small.
Cleans effectively, even without detergent
Car brush works well to clean the car (again, without detergent so far)
I can't think of anything else that would be effective in cleaning the back patio
Expensive and extravagant to run off the water main and suction hose is infuriating
Not good on a block driveway where the cracks are filled with kiln-dried sand (which they need to be to promote drainage)
Detergent dispenser appears to be temperamental, to say the least
Jan 2016 update: The cars constantly get filthy in winter and, with a seemingly endless supply of rainwater in the water butts, it is a quick job to use the vary-lance and brush attachment to clean them. Today the machine stopped delivering water. At first I suspected an air-lock or sediment blockage in the hose from the water butt but that was siphoning water fine. I decided it was probably a blockage in the machine itself so fetched the garden hose (packed away in the shed for winter). That sorted it out but it's another indication of the machine's limitations. Once it was working again I reverted to rainwater and cleaned both cars and much of the patio.