What limescale is and why makers warn about it

Limescale is a hard, chalky deposit made mainly of calcium carbonate¹. You've probably seen it as the white crust inside a kettle or around a faucet.

Where it forms

Limescale often builds up in kettles, boilers and pipework, and most of all where hot water is used¹. Hard water is the supply. The more calcium and magnesium the water holds, the more material there is to leave behind. See what water hardness means for the numbers.

Its color depends on what else is in the water. It can run from off-white through greys to pink or reddish-brown, and iron compounds give the reddish browns¹.

What it does, in general

Wikipedia says that besides being unsightly and hard to clean, limescale can seriously damage or impair the operation of various plumbing and heating components¹. Two effects are described for equipment in general:

• Scale build-up restricts the flow of water in pipes².
• In boilers, deposits impair heat transfer to the water and reduce heating efficiency².

Those are general statements about plumbing and boilers, not about any one espresso machine. The makers' own words come next.

What makers say

Breville. Over time, minerals from hard water can collect inside the machine, according to Breville's support page. It lists brewing flow, temperature and machine performance among the things that buildup can affect³.

Its blog lists symptoms you might link to scale. Low or inconsistent water pressure could be a sign of scale buildup inside the reservoir or internal tubes⁴. Lukewarm shots might point to mineral buildup in the reservoir or pump, the blog says, though it also names a thermostat or heating element as other possible causes⁴.

That last point matters. A weak or cool shot doesn't prove there's scale. Follow the troubleshooting steps in your manual, and contact the maker for anything that needs the machine opened. Don't open it yourself.

Decent Espresso. Heater failures are the company's stated worry, and it links them to scale buildup from unsuitable water⁵. It also explains why scale is a concern for its machine. It has many small tubes and calibrated pressure-restricting orifices, so avoiding scale is particularly important⁵. At the same time, it says the machine is intentionally designed to reject scale and deposit it harmlessly in the water reservoir⁵.

What scale doesn't tell you

Scale is about equipment. It isn't a statement on whether water is fit to drink. For questions like that, ask your water supplier or a doctor.

Removing it

Descaling agents are commonly used to remove limescale¹. Which one is right depends on the machine. One maker's guide allows only citric acid for its machines and says it can't guarantee that other descaling agents won't damage components⁵. Another maker tells you to use its own recommended solution⁶.

So don't pick a product from a general article. The page on descaling and the manual explains where to look, and what makers say about water covers the water side.