The Heating Element

The resistive heating element is simply a coiled wire, very similar to the filament of a light bulb or the element in an electric toaster, that gets hot when you run electricity through it. In a resistive element like this, the coil is embedded in a plaster to make it more rugged. The heating element has two jobs:

  1. When you first put the water in the coffee maker, the heating element boils it.
  2. Once the coffee is made, the heating element keeps the coffee warm.
In the following pictures, you can see the connection between the heating element and the warming plate. The heating element presses directly against the underside of the warming plate, and a white, heat-conductive grease makes sure that the heat transfers efficiently to the plate. This grease, by the way, is extremely messy (very hard to get off of your fingers!). You find this grease in all sorts of devices, including stereo amplifiers, power supplies -- pretty much anything that has to dissipate heat.

The coffee maker heating element and warming plate
The coffee maker heating element and warming plate
The coffee maker warming plate
The coffee maker warming plate
The coffee maker heating element by itself
The coffee maker heating element by itself

The coffee maker's switch turns power to the heating element on and off. To keep the heating element from overheating, there are three solid-state temperature sensors, as shown here:

The coffee maker's solid-state temperature sensors
Simple solid-state temperature sensors cut off the current when things get too hot.

The device attached directly to the coil is the primary temperature sensor. When it detects the coil getting too hot, it cuts off the current. Then, when it cools down, it turns the coil back on. By cycling on and off like this, it keeps the coil at an even temperature. The other two devices appear to be thermal fuses. They simply cut power if they sense too high a temperature. They are there for safety reasons, in the event that the main sensor fails.

One part that is not visible in this coffee maker is a one-way valve. This valve is either in the hole in the bucket or in the aluminum heating pipe. If there were no one-way valve, then the boiling water would be just as likely to flow back into the bucket as to rise up the black tube. The one-way valve lets cold water into the aluminum tube, but forces the bubbles of boiling water to flow up the black tube. If you blow on the tube leading into this value, the valve should be open. If you inhale through the tube, the one-way valve should block any air.