I didn't see any obvious problems until the third time I took the heating wand apart and saw signs of significant heat damage.
|The old, broken, charred heating element
The white heating element plug has a pin crimped to a white wire on one side which in turn connects to a thermal protector (the white rectangle) and then to one end of the heating element.
On the other side, the heat-damaged side, the plug has a pin crimped to a steel(?) rod (the black rod above), delivering power to the tip of the heating element (on the right).
The rod is charred and pitted. The inside of the plug is severely scorched. The crimp was very loose and I suspect either corrosion resulting in increased resistance and high heat, and/or loose crimp resulted in arcing.
|Replacement. Pic from sparkfun.com
I'm a bit skeptical of the safety and reliability of the original design so I ordered a replacement from Sparkfun with a different design. The heating coil is connected with wires instead of steel rods.