How to descale a kettle with citric acid

Citric acid is a cheap, food-safe, odourless way to dissolve the limescale (calcium carbonate) that builds up in kettles in hard-water areas. It works faster than vinegar and leaves no smell or taste behind.

What you need

Citric acid powder (food grade)
Water
A soft brush or non-scratch sponge (optional)
A cloth for drying the outside

Amounts

Kettle size	Water	Citric acid
Small (up to 1 litre)	500 ml	1 tablespoon (about 15 g)
Standard (1.5–1.7 litres)	1 litre	2 tablespoons (about 30 g)
Heavy scale, any size	Fill to the minimum line plus a little more	Increase to 3 tablespoons (about 45 g) per litre

As a rule of thumb, use roughly 30 g of citric acid per litre of water. Always use at least enough water to cover the element or the heated base plate and to reach the kettle's MIN line.

Method

Empty the kettle and rinse out any loose flakes of scale.
Add the water (see amounts above), making sure it is above the MIN line.
Boil the water once, then switch the kettle off.
Add the citric acid to the hot water. Add it slowly: it will fizz as it reacts with the scale, and adding it to boiling water all at once can make it foam over.
Leave it to soak for 15–20 minutes. For heavy scale, leave it for up to 1 hour, or reboil once and soak again.
Pour the solution away down the sink. It is harmless to drains and will help clean them.
Scrub any remaining spots gently with a soft brush or sponge. Never use metal scourers on the element or the inside of a stainless-steel kettle.
Rinse thoroughly. Fill the kettle with clean water, boil it and pour it away. Do this two or three times so no citric acid remains.
Wipe and dry the outside of the kettle.

How often to do it

Water hardness	How often
Hard water (much of London, the South and East of England)	Every 2–4 weeks
Moderately hard water	Every 1–2 months
Soft water	Every 3–6 months, or when you see scale

Descale sooner if you notice white flakes in drinks, a chalky film inside the kettle, a louder or slower boil, or the kettle switching off early. Regular descaling keeps the kettle efficient: scale insulates the element, so a scaled kettle uses more energy and takes longer to boil.

You can also descale the kettle's filter (usually behind the spout) by soaking it separately in a small bowl of the same warm solution for 15 minutes.

Safety notes

Unplug the kettle before handling the base, the element or the filter, and keep the base and electrical contacts dry.
Watch out for foaming. Adding citric acid to very hot water can make it fizz up suddenly. Add it gradually and never fill the kettle above the MAX line.
Do not reboil an unattended kettle while it contains the solution; foam can reach the lid and the switch.
Handle hot water carefully when pouring the solution away. Let it cool for a few minutes if you prefer.
Rinse well before using the kettle for drinks. Citric acid is food safe, but leftover solution will taste sour.
Keep citric acid powder away from your eyes. It is an irritant; if it gets in your eyes, rinse with plenty of clean water. Store it out of reach of children.
Don't mix it with other cleaners, especially bleach or other chemical descalers.
Check the manufacturer's instructions first. Some kettles (for example ones with special coatings, or some aluminium kettles) may not be suitable for acid descaling. Never put a kettle base or a corded kettle in water.

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