The final major piece of maintenance I wanted to perform on my espresso machine was to descale the boiler. I knew nothing about the quality of water that the previous owner had used with this machine.

I removed the pressure gauge fittings of each boiler and filled them with a pretty aggressive citric acid solution, then flushed them a few times until the water ran clear.

The first few flushes were blue from some of the oxidized copper.
The blue had gone away at this point, but some scale deposits were still making the water cloudy.