I purchased this model in Feb 2009, and a stack of replacement filters. The instructions suggested I change it every 2 months, but now (oct2010) the unit harldy delivers any steam.
As with the other reviewer it seems that the pipes have been clogged by something to stopnthe water getting through.
I did open the unit up, and found the heart of this unit is a factory sealed heating unit, which you should not open up unless you have the resin to reseal it..
This heating chamber heats it up and delivers the powerful steam that makes the job so easy.
So there is no way of descaling this unit without causing further damage, second option is to replace the part, but then what if the small water pump is also plagued by limescale (it too is nosier than before) and due for imminent failure. So I face the dilemma of changing parts or for around the same money buy a new one. And out the 10 or so filters left to good use, or should a buy a new model altogether.
Overall the quality and ease of use is great, slows down with age but definitely wroth £70, but not £140.. I suggest buy a better reliable model if youre gonna spend this much