How to descale a kettle and stop limescale coming back

15 minutes of work, 20 minutes of waiting. Costs a few cents.

Try this first (costs nothing extra): fill the kettle halfway with half white vinegar and half water, boil it, switch it off and leave it for 20 minutes. Pour it out. Rinse. Boil fresh water and throw it away, twice. Done for most kettles.

What the white crust is

Limescale is mostly calcium carbonate left behind when hard water heats up and evaporates. It is not dirt. It is rock, in thin layers, and it dissolves in mild acid. That is why vinegar and citric acid both work.

Small flakes are generally not a health concern, but they dull the taste, coat the element and makes the kettle take longer to boil. ## Before you start

• Unplug the kettle and let it cool completely.
• Read the manual. Some makers recommend citric acid only, or warn against vinegar on certain finishes.
• Use one product at a time. Never mix descalers, vinegar and bleach in the same kettle or sink. Poison centres warn that some cleaner combinations release harmful gases. See the Missouri Poison Center note on mixing cleaners.
• Open a window. Hot vinegar smells strong.

Run the vinegar soak

1. Fill the kettle to about half with equal parts white vinegar and water. Stay below the max line.
2. Bring it to the boil, then switch it off.
3. Leave it 20 minutes. For thick scale, leave it an hour.
4. Pour it out and look. Loose flakes will have lifted.

If that does not work

Thick, old scale needs a second round or a stronger acid.

• Repeat the soak with fresh vinegar mix. Two rounds beat one long soak.
• Try citric acid. A couple of teaspoons of food-grade citric acid powder in a half-full kettle of hot water, left for 30 minutes, is a common alternative. It is odourless.
• Scrub the stubborn edge with a soft brush or a cloth. Do not use steel wool or a knife. Scratches hold scale and bacteria.

If you want a tool, a packet of citric acid or a descaling powder is the only thing worth buying. Match it to your kettle material and follow the label. Skip it if vinegar already worked.

Rinse, then rinse again

This part decides whether your next coffee tastes of vinegar.

1. Rinse the inside with cold tap water.
2. Fill with fresh water, boil, pour away.
3. Repeat once more.
4. Taste a spoonful of the third boil. If it still tastes sharp, boil once more.

Which acid to pick

Both work. Pick by what you have and what you can stand.

• White vinegar: already in the cupboard, cheap, strong smell. Needs the extra rinses.
• Citric acid powder: no smell, rinses clean, costs a little more. Better for glass and plastic kettles, and for a kitchen with no ventilation.
• Kettle descaler tablets or liquids: fine, if the label says it suits your kettle. Follow the dose on the pack and do not add anything else to it.

Never top up with a second product halfway through. If the first did not work, rinse the kettle fully before trying another.

Slow the scale down

Scale returns faster in hard water areas, and nothing stops it fully.

• Empty it after use. Standing water leaves the crust. Boil only what you need.
• Wipe the base with a cloth once a week when it is dry.
• Descale on a schedule. Monthly in hard water, every few months in soft water, or when you see white flakes.
• Use a filter jug if your water is very hard. It softens the taste and slows the crust, though it does not remove it entirely.

Fix it, replace it or live with it

• Fix it: white crust, slow boil, flakes in your tea.
• Replace it: the element is corroded or rust coloured, the base leaks or the plastic is cracked.
• Live with it: light haze on a stainless base that does not touch the water you drink. Wipe it and move on.

For the other common kitchen grime problem, see the pan you should stop scrubbing. For something on your feet instead, start with sore feet after work.