Cuprajake
If it’s just KHCO3, just as with NaHCO3 it won’t scale so long as there are no Mg or Ca ions present. Otherwise, over a period of time of use in the service boiler, scale will always start to form unless you drain it. I add Mg for improvement to the taste perception and body.
LMSC Please forgive my curiosity. How does this work ?
I remove the anti-vac valve and syphon off the water, then pour distilled in and put the valve back on. This stops me from having to faff about with the water tank and means I don’t need to descale. I could drain through the hot water tap but then I’d have to heat it up and that seems like a waste. Removing the valve on mine was always easy and, of course, it’s only four or five screws to remove to access the boiler so it’s quicker than using the pump and less noisy and I don’t get the distilled water anywhere but where I want it. It gets topped up with the water tank remineralised to 30 GH and 40-50 KH hence the need to drain. I wouldn’t drop hardness completely for the sake of avoiding this, and I certainly wouldn’t decrease alkalinity, as there’s little point spending over £1k on a machine and buying expensive coffee only to then sacrifice the quality so the little trouble-free maintenance I have to do can be avoided. What would be next? Not using it so you don’t have to backflush.