Removed the boiler from my Gaggia Classic and it was a humbling experience to learn just how much scale can build up even on RO water.
Ultimately wasn’t able to get the boiler looking squeaky even after 2 hours of sitting in descale solution. Is that probably fine? I just rinsed and brushed it until I didn’t see any more visible scale flakes coming off. Flow is back to normal as far as I can tell.
Agree with checking membrane but also using just pure RO can be corrosive to metal parts. Wonder if some of this is more corrosion than scale. Checking pH and KH level as and optimizing these often with just a splash of tap water moxedin the reservoir can help and might even make coffee taste better too