Boiler scale prevention and water path

How scale forms in espresso machine boilers, the water path it follows, and strategies to prevent buildup and maintain performance.

Coffee Basics Nerds
July 9, 2025
2 min read

Article 6 of 12 in Espresso Machine Technology/

The Water Path in Espresso Machines

Water enters from mains or reservoir.
Passes through softening/filter system (if installed).
Enters pump (rotary or vibratory).
Flows to brew boiler (or heat exchanger) for brewing water.
Steam boiler (if separate) heats water for steam and hot water taps.
Brew water passes through grouphead before extraction.

Scale Formation

Cause: Precipitation of dissolved minerals (calcium, magnesium) when water is heated.
Locations: Boiler walls, heating elements, pipes, valves, solenoids.
Effects:
Reduced heat transfer efficiency.
Blocked water flow, erratic pressure.
Corrosion under deposits.
Costly repairs and downtime.

Prevention Strategies

Water Filtration & Conditioning:
Carbon filters: remove chlorine and particulates.
Ion-exchange softeners: reduce hardness (Ca²⁺, Mg²⁺).
Reverse osmosis with remineralization: precise control of hardness and alkalinity.
Descaling Protocols:
Periodic chemical descaling (citric or proprietary solutions).
Requires caution—can damage seals if overused.
Monitoring:
Measure hardness, alkalinity, and TDS regularly.
Follow SCA water specs: total hardness ~50–175 ppm, alkalinity ~40–75 ppm.

Best Practices

Use proper filtration at installation based on local water.
Replace filters and cartridges on schedule.
Avoid overly soft water (<30 ppm hardness) which risks corrosion and flat taste.
Train staff to flush boilers and groupheads daily.

Summary

Scale prevention begins with understanding the water path and managing mineral content. Proper filtration, scheduled descaling, and water testing protect boilers, extend machine life, and ensure consistent espresso quality.

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