After a lifetime owning a kettle, some have started to wonder why it randomly makes a clicking sound when it’s not in use – and it turns out there’s a reason for it
Most of us don’t think twice about the sounds our kettle makes, but there’s a curious phenomenon that has some questioning their everyday appliance.
A Reddit user sparked a bit of a virtual discussion by asking: “Why do electrical kettles make a click noise when they are off? Every now and then my kettle makes a click noise when its off”.
They’re not alone in their ponderings, as confirmed by another user who shared: “I have often wondered this about mine too – its usually several hours after I used it and turned it off.”
Thankfully, the mystery was unraveled by water specialist Professor Stuart Khan from the University of New South Wales. Chatting with ABC News, Professor Khan explained that this clicking conundrum is typical in hard water regions.
Here’s his take: “Hard water behaves differently to soft water because as water is heated, the hardness becomes less soluble. I expect the combination of these two things leads to the more violent bubble-collapsing process.”
He pinpoints the origin of the clicks to bubbles forming and popping beneath the surface prior to their ascent. Expanding on this, Professor Khan notes: “The reason why this happens more in areas where there is hard water is not because of the calcium or magnesium causing the popping – but rather they cause a build-up of scale on the inside of the kettle. The scale is brittle, and the tiny particles break off and those are now aerating the water more.”
Redditors seemed equally as clued-up about the mystery. One user, dispensing a drop of science, explained: “Kettles use a ‘bimetallic’ element to gauge temperature. Two different pieces of metal with two different temperature expansion rates. As they both heat up, they both expand, but one more than the other, so they curve, making an electrical circuit connection that switches off the kettle. After a certain amount of time they contract back and reset, just like how when you drive your car and then get out you can hear the engine clicking as it contracts.”
Adding another layer, a different user chimed in with: “Materials (like metal for example) expand when heated and can shift against fixings like rivets, or other components in the frame. This can cause clicking both while heating and while cooling.” Meanwhile, yet another commentator simplified the concept by saying: “Thermostat. It expands when hot and contracts when it gets cooler. It’s the different metals used that move on each other.”
