by orphanespresso on Sat Mar 12, 2011 11:55 pm
On the face of it I would say it is bad luck...but there may be more going on as you have possibly changed electrical grids lately.
The question is WHY does an element burn out in the first place? I know that you are both observant and careful so it likely is not due to running out of water and melting it down but look at Ohm's law, v=ir (voltage =current x resistance). This equation ALWAYS stays in balance in any circuit. Now, when a resistor (heating element) is cold, the resistance is LOWER than when it is warm or hot. Since the r variable goes down, given the same voltage the i or current will increase when the element is cold vs the rated resistance. This is the reason that a light bulb always burns out when you switch it on, the filament (resistor) is cold and therefore is momentarily exposed to more current than usual, and if the filament has become thinned due to loss of metal molecules over time then pffft, the filament burns through at some weak point due to the increased current on the wire.
Then, consider the electrical grid...where we are our voltage ranges from 115 to about 125 volts so given the constant resistance of the heating element as a factor of temperature (and geometry of the resistor), then the current will be different at these different voltages by ohm's law once again. So take a worst case scenario when the element is cold and you turn on the machine right in the middle of a power surge, the effect on the element or resistor would be amplified. This is one good reason to plug the machine in through a surge protector just in case, to hopefully avoid this scenario.
Ideally, the element would be slowly brought up to power by use of a variac type approach when you slowly bring up the current until the element is warm enough to run on the rating but that is a bit extreme.
Also, check to see if the element is actually burned....may just be shorted at the terminal ends and can be fixed.