The Classic Pro's boiler is cast aluminum — fast-heating, but chemically more sensitive than the stainless boilers on some other machines. Both over- and under-descaling cause real problems on this specific model, so getting the balance right matters more than usual.

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01Why aluminum boilers need a gentler approach

Aggressive, high-concentration acidic descalers can etch cast aluminum over repeated use. At the same time, skipping descaling lets scale flake off internally and clog the 3-way solenoid valve. Use a citric-acid based descaler at the manufacturer's specified dilution — never stronger "to be thorough."

Avoid this mistake Don't substitute a generic heavy-duty descaler meant for stainless boilers. If a product doesn't specify aluminum-safe use, check with the manufacturer or choose one that explicitly is.

02Standard descaling process

  1. Empty and refill the water tank with descaling solution mixed per the product's instructions.
  2. Run the solution through both the group head and steam wand in cycles, following your descaler's specific instructions for cycle count and duration.
  3. Flush thoroughly afterward with multiple full tanks of plain water through both outlets.

03Backflushing the solenoid valve

Separately from descaling, backflushing clears coffee oils and sediment from the group head and helps keep the 3-way solenoid valve moving freely:

  1. Install a blind basket (a solid basket with no holes) in your portafilter.
  2. Add a half-teaspoon of Cafiza or similar espresso machine cleaning powder to the blind basket.
  3. Lock the portafilter in and run the brew switch on, then off, repeating 5-6 times — you'll see discolored water expel from the solenoid drain each cycle.
  4. Remove the blind basket and run several plain-water cycles to rinse thoroughly.
How often Backflush weekly with regular home use; descale based on your water hardness — see our general descaling frequency guide for hardness-based intervals.

If you're experiencing water only coming from the steam arm, a stuck solenoid from sediment buildup is a likely cause — backflushing is the first thing to try.