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Buildersmate, this is what Quooker told me:
You can buy a cartridge that attaches to the tank and the cartridge collects the limescale before it enters the tank.
For me, the downside to this is the cost per cartridge (£90) - and this could be as often as every 18-24 months. However my sister's view is that it is a small price to pay for the convenience of having a boiling water tap. :o/
You can have it serviced by a Quooker rep who will do the descaling for you, and in hard water areas an annual service is recommended. Labour costs are high and although I can't quote the exact charge, I think it was somewhere in the region of £150 (another "ouch" moment for me. I'm a Yorkshire lass). :o)
The third option is that Quooker will send you free of charge, every twelve months, a 'do-it-yourself' descaling kit (presently free of charge but I expect that will change in the future, although the rep told me they have no plans to change this).
As you mention, the tank is difficult to access, and has to be uninstalled and disconnected, and this sounds like quite a task (which is why I asked in my OP, if anyone has cleaned their own tank). I've watched it being done on YouTube, as has my husband, who tells me he's happy to 'have a go', but if it proves too much hassle we'll go down the cartridge route.
I expect many folk will think....'Bu 88er that, I'll stick with the kettle'. I would've thought that too, had I not experienced its convenience.