Simple versions of Kettles

The humble kettle has been given a new image in recent years. Simple versions consisting of only a container with a heating element fixed inside are still available, but for many years the trend has been towards the automatic kettle that turns off once the water has boiled.

Some more recent models have been further improved with high-speed elements and spout filling. The latest jug version combines all the features of a modern kettle with the added feature of the handle’s being positioned on the side, so that the user avoids the steam when pouring.

As with irons, cable damage through wear and tear and misuse tends to be a common fault. Cordless kettles and jugs preempt this problem. They are similar to cordless irons in that they require a power base that has its own mains lead. When the cordless kettle is placed on its base, electrical contact is made to its heating element. The operation from then on is like any other automatic kettle.

There are three types of kettle: basic, automatic kettle and automatic jug. They all work in much the same way, apart from added refinements and styling. Some common problems apply to all three types, whereas others are specific to one.

Basic kettles

A sealed heating element is fixed within the kettle. This starts to heat up once the connecting mains lead is plugged into its 13 amp three-pin socket and switched on. As the kettle has no isolating switch of its own, it is essential that the element is covered with water before plugging in and switching on. The water will continue to boil until the kettle is manually switched off. Most, however, are fitted with a boil-dry protector to prevent the element melting if the kettle is left switched on.

If overheating does occur, either because the kettle has boiled dry or because it was switched on without having any water in it, a mechanical, thermally-operated device is activated. The operation of this safety device releases a powerful spring and rod that ejects the mains lead from its socket at the rear of the kettle. Some kettles can be reset when the element has cooled down, but others, once activated, cannot be reset and need a new element to be fitted.

Replacement elements for these kettles are widely available and are supplied with fitting instructions. Make sure that the correct size and shape of element is obtained and renew all seals and washers at the same time. It is not advisable to fit old seals to new elements. Check earth continuity of the kettle and the socket earth path. Fill the kettle with water and leave it to stand for a short time to confirm there is no seeping or leaking before carrying out a functional test. Look closely for poor connections in the socket on the kettle lead and renew at the first signs of any problems.

Automatic kettles

Heating is similar to the basic kettle with the added bonus of its switching off automatically once the water has boiled. This simple operation has many variations, but nearly all types use a bi-metal strip. The kettle usually has a biased on/off switch or button which, whenturned or pushed to the on position, supplies power to the element to start the heating process. Steam produced by the boiling water is directed on to the bi-metal strip which then bends. The corresponding movement is transferred to the switch button and trips the biased switch into the off position.

Two versions are commonly used: vapour stat and steam stat. The vapour stat allows steam to escape through a small hole at the top of the kettle. The hole directs the steam directly on to the bi-metal strip. The mechanical action of the bi-metal is transferred to the switch by a rod, thus keeping water vapour away from the switch device.

Steam stat-controlled kettles have a special element with an open-ended tube fitted to it. The open end of the tube is designed to be above the normal fill level so that when the water boils, steam is forced down the tube and on to a bi-metal strip, the mechanical action of which operates the kettle switch as before. This type of control allows the switch unit to be lower down on the kettle and generally much smaller. Problems may occur if water is trapped in the steam tube through incorrect filling or misuse. This stops or impairs the transfer of steam to the bi-metal strip and affects the auto-switching. Allow the kettle to cool, empty the contents and invert the kettle to drain the tube. Like basic kettles, auto kettles have a separate thermally operated safety device for protection.

Conversion kits are available which convert the basic kettle into an automatic steam stat operation. The kit consists of the element and stat switch

Jug kettles

Jug kettles operate in the same way as auto kettles, with different models and makes using vapour or steam stats. The switch action on the vapour stat version may involve a long, push-rod operation to actuate the switch situated within the handle. Again, a thermal safety device is fitted.

The element inside the kettle is smaller, but its wattage is still usually around 2W, enabling it to boil up to 1.7 litres (3 pints) of water quickly. Much of the early promotion of jug kettles concentrated on their ability to heat only the amount of water required, thus saving energy. This in itself was admirable, but posed a design problem. After the kettle had been filled, the water boiled as normal and then if all the water was emptied out, the residual heat within the smaller and tighter wound element could not be dissipated. This would cause early failure of the jug element if it happened regularly. It would also result in repeated tripping of the thermal safety device (resettable on most jug kettles).

Common problems

The bi-metal strips on most appliances are adjustable to allow for limited boiling time before ‘switch off’. Do not attempt adjustment until all other possibilities have been investigated.

Do not make any adjustments or repairs, descale or even fill any kettle while it is still plugged in. Isolate completely: switch off, plug out.

In common with all appliances that heat water, scale will be produced. The level of build-up differs from area to area. Regular descaling is recommended to avoid premature failure of the element and to improve the efficiency of the kettle. Frequency depends on the hardness of your local water supply. Do not be tempted to chip at the scale within the kettle with a sharp instrument. Use a descaler designed specifically for kettles and read all instructions for the product before descaling.

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