Plainwire / Guides / Kettle will not switch off

Kettle will not switch off

Revised 2026-08-11 · rev 9 · hexnut · 25 min · low difficulty

A kettle that boils and keeps boiling has a fault in its steam path, not in its element. The element is doing exactly what it is told; nothing is telling it to stop.

Almost every corded kettle sold in the last thirty years switches off the same way. Steam rises from the water, travels up a narrow channel moulded into the handle or the body wall, and reaches a small bimetallic disc sitting in the base of the switch assembly. The disc snaps at around 98 °C, pushes a plunger, and drops the latch that holds the switch on. Three things break that chain, and they break in a predictable order.

Diagnose before you order anything

1. Check the lid seats. Most kettles will not switch off with the lid open or ajar, because the steam escapes instead of going up the channel. Fill, close the lid firmly, and listen for the catch. If yours has a push-button lid release, look at whether the button is still returning fully.
2. Look for steam escaping where it should not. Boil it and watch the handle and the seam between body and spout. A visible plume from a joint means a cracked channel or a perished gasket, and the disc is never seeing the steam.
3. Check the fill level. Overfilled kettles spit water into the steam channel. Water in the channel does not carry heat to the disc the way steam does. If it only misbehaves when full, this is your answer and there is nothing to repair.
4. Only then suspect the disc. A tired bimetallic disc switches late or not at all, and it is the part that fails after roughly a decade of daily use.

Getting into the base

The switch assembly lives under the base plate. On most models the plate is held by three or four screws under the rubber feet or under a foil label; on a minority it is clipped, and the clips break if you are impatient with them.

Photograph the switch assembly before you disturb it. There is usually one spring, and it will go somewhere you cannot see the moment it is free.

The part

The disc is not sold on its own by anyone reputable. What you buy is the complete thermostat unit — usually a Strix-pattern or a compatible clone — and it is a stamped part with a code on it. Match the code, not the kettle. The same unit appears under a dozen brand names and the same brand will use three different units across its range.

The two numbers that matter are the disc temperature (98 °C is the common one) and the terminal orientation. Getting the orientation wrong means the lid-switch lever no longer lines up, and there is no way to correct it once fitted.

Refitting

1. Seat the new unit dry. Do not use sealant. The channel needs to breathe and the original design has no sealant in it.
2. Work the switch by hand before closing up. It should latch with a definite click and release cleanly when you press the plunger with a matchstick.
3. First boil outdoors or over a sink. Half fill it. If the switch was fitted a fraction proud, the kettle will boil dry, and you would rather discover that somewhere you can unplug it quickly.

When it is not the thermostat

Two failure modes look identical from the outside. A welded contact in the switch itself will hold the kettle on even after the disc trips — you can hear the trip and nothing happens. And a lid that no longer closes the interlock will, on some models, keep the boil-dry protection from arming. Both are visible once the base is off; neither is fixed by the part you probably already ordered.

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