Question 1

How does an electric kettle know when to switch off?

Accepted Answer

Through a **bimetallic strip** and a small steam channel — an entirely mechanical arrangement with no electronics or temperature sensor involved.

**The bimetallic strip** is the key component. It is two different metals bonded together, chosen because they expand at different rates when heated. Because one side expands more than the other, the strip has no choice but to **bend** as it warms. Heat it enough and it snaps decisively to a curved position, and that movement physically opens the switch contacts.

**The clever part is where the steam goes.** A kettle does not measure the water temperature at all. Instead, a narrow tube runs from just above the water level, up through the handle, to a small chamber containing the bimetallic strip — usually near the base of the handle or under the lid catch.

While the water is heating, little steam is produced. Once it reaches a rolling boil, steam is generated rapidly, travels up the channel, and floods the chamber. Steam at 100°C heats the strip quickly, it flexes, and the switch trips.

So the kettle detects **boiling** rather than temperature — a much simpler and more reliable thing to sense mechanically.

**This explains several familiar behaviours:**

**Leaving the lid open stops it switching off.** Steam escapes rather than being channelled to the strip. Kettles have a separate **dry-boil protection** thermostat in the base as a safety backstop.

**A kettle boiling at altitude** switches off at a lower temperature, because water boils cooler — it is still detecting boiling, just boiling at 90°C.

**Blocked or limescaled steam channels** cause a kettle to boil on and on, one of the most common faults.

**A second bimetallic thermostat** clamped against the heating element protects against boiling dry, cutting power if the element overheats. The same principle appears in irons, toasters and older thermostats.

Question 2

Why do kettle elements fail, and does limescale matter?

Accepted Answer

Kettles fail for a small number of predictable reasons, and limescale is the underlying cause of most of them in hard water areas — through a mechanism that is more specific than "it clogs things

Question 3

Is a boiling water tap cheaper than a kettle?

Accepted Answer

On energy alone the difference is small and can go either way; the honest case for one is convenience, and the honest case against is the cost of ownership. How they work. An insulated tank under the

Question 4

Is it bad to boil water twice in a kettle?

Accepted Answer

For ordinary tap water, no. The claim that re-boiled water is harmful circulates widely online and does not hold up for the water most people are drinking. The argument usually runs that boiling

Question 5

How does a pressure cooker work, and is it safe?

Accepted Answer

By raising the boiling point of water above 100°C, so food cooks at a higher temperature and therefore much faster — and modern ones are considerably safer than their reputation, which derives from

Question 6

What is a combi microwave, and what does a steam oven do?

Accepted Answer

They are two different attempts to combine cooking methods in one appliance, and they solve different problems. A combination (combi) microwave adds conventional heating to microwave cooking.

Question 7

How do I remove limescale from a kettle?

Accepted Answer

Limescale is calcium carbonate left behind when hard water evaporates. It is harmless to drink but insulates the heating element, so a scaled kettle takes longer to boil and uses more electricity,

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