Kettle Not Switching Off When Boiled

Kettle Not Switching Off When Boiled? Here’s why…

All most of us know about electric kettles is, you fill them with water, switch them on and the water boils. To keep them running efficiently we give them a descale every so often. So assuming that’s the extent of your knowledge of the inner workings of an electric kettle, let’s look at the electric kettle a little closer.

We need to ask and find the answer to a few questions to understand what’s going on with our electric kettle. Firstly how does an electric kettle create heat? Why does a kettle get limescale? And how does a kettle know when to turn off?

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How Does An Electric Kettle Create Heat?

The kettle produces heat using the principle of resistance. An electric current is passed through a metal plate, the metal resists the current which causes the plate to heat. That heat is transferred to the water and in time it boils. Here’s an interesting fact, boiling point is not constant.

The temperature needed to boil water varies according to altitude. For instance at sea level water boils at 100 C (212 F) but at 1 mile above sea level, water will boil at 94 C (202 F). Knowing this means we can work out that a kettle’s cut off point has nothing to do with a thermometer or temperature control. 

Why Does A Kettle Get Limescale?

Water collects minerals as it travels through bedrock, in areas of chalk or limestone, the water collects more minerals. Once the water is subjected to heat and begins to evaporate, those elements turn into solids again. They collect on the inside of the kettle and we identify them as limescale.

How Does A Kettle Know When To Switch Off?

kettle not switching off when boiling

This is so clever and yet so simple, once you get your head around it. It’s not a thermometer that controls the kettle, it’s a thermostat. How it works is, 2 different types of metal are bonded together, one has a faster expansion rate than the other under heat. Steam from the boiling water passes over the bimetallic thermostat and the metal changes from a curved position to a curve in the opposite direction.

When the thermostat snaps open, it flicks a switch that cuts the power (like a circuit breaker) and the kettle stops boiling. The steam is introduced to the bimetallic strip via a small tube situated either inside or alongside the handle. There’s a small opening right at the top of the handle inside the water chamber.

As the water boils, it produces steam, this steam travels through the small hole, along the tube and then over the bimetallic strip. Once the steam is hot enough the strip reacts and the switch is activated.

Why Does The Electric Kettle Not Turn Itself Off?

Kettle thermostat

You’ve probably worked it out for yourself now, but let’s go through it anyway. Over time, even with regular kettle descalers, that little hole at the top of the kettle will get clogged with limescale. Possibly not fully clogged (although sometimes that’s the case) but just enough to prevent enough steam from entering the pipe that leads to the thermostat. Not enough steam means no metallic reaction, and the kettle doesn’t turn off.

How To Repair A Kettle That Doesn’t Switch Off When Boiling

We don’t advise you to take the kettle apart, and we definitely don’t want you messing with anything electrical. If this tip doesn’t work, we strongly suggest you invest in a new kettle, in fact, check your guarantee, you might find it’s still on warranty, in which case just send it back to the manufacturer. If, however, the warranty period is over and you want to give it a go, be sure to unplug the kettle first, safety first always.

So, with the kettle unplugged and the socket switched off, open the lid of your kettle. If you look closely near the top of the kettle on the opposite side to the spout, you should see a small opening. In ours it is a small oblong shaped opening (other makes and models vary).

Take a cotton bud, soak it in descaler, and push it into the hole as far as you can. Take care to not let go of it as it will block the tube if it falls inside, and possibly be a fire hazard. Leave the descaler to work for at least a couple of hours and then take a fresh cotton bud, wet the tip with tap water, and wipe all around and inside the hole to remove any descaler residue. Again making sure not to lose the cotton bud down the tube.

Repeat this rinsing 3 times in total, then fill your kettle and boil it. With any luck the automatic cut out will work and you’ve added another skill to your repertoire. If it still doesn’t switch off, it’s definitely time to buy a new kettle.

Frequently Asked Questions

How do kettles know when to stop boiling?

Kettles know when to stop boiling because they have a small thermostat situated just below the base of the handle. This thermostat is triggered by steam travelling down a small tube that starts at the top of the kettle by the handle. Once the water starts to boil, it creates enough steam to trigger the thermostat which consists of a bimetallic strip. This changes shape when hot enough and that movement triggers the cut out switch.

What happens if a kettle keeps boiling?

If a kettle keeps boiling what happens is the water will eventually boil away.

Are electric kettles safe?

Electric kettles are safe if used correctly. Never overfill and never allow to boil dry.

Where is the thermostat in a kettle?

The thermostat in a kettle is situated at the bottom of the kettle integrated with the heating element.

Why is the heating element of an electric kettle at the bottom?

The heating element of an electric kettle is at the bottom because this allows you to boil less amounts of water. If the heating element was at the top of the kettle you would always have to boil a full kettle of water even if you only needed one cup.

How hot is boiling water from a kettle?

How hot boiling water is from a kettle is dependent on the altitude the kettle is being used at. At sea level water boils at 100 C but at 1 mile above sea level water boils at 94 C.

Why can’t water go above 100 degrees?

Water can’t go above 100 C because at 100C it starts to evaporate. This means it changes from a liquid state to a gas, in this case steam.

A Short History Of The Kettle

Over 5,000 years ago the Mesopotamians used a vessel that resembles the shape and form of a kettle to boil water. These first kettles were made from bronze, then over the centuries it was discovered that kettles could be made from iron and they could be placed directly into the fire on the flames. 

Jump forward to 1891 and the Carpenter company in the USA developed the first kettle powered by electricity. It wasn’t that popular as it took nearly 12 minutes to boil the water due to the heating element and the water being kept in different chambers. In 1922 the Swan company developed the first electric kettle with an integrated heat element.

Nothing much happened with the design until 1956 when the British company Russell Hobbs introduced the automatic kettle. This design led to where we’re at today with glass kettles, metal kettles and plastic kettles all turning off automatically.

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