LTC3112: Limited Output Current
Assuming that you went through all of the proper component selecton (for a DC to DC converter, all the components must be selected by guidelines listed in the datasheet) (you cant use any inductor or capacitor you want) 

With a setup like that, the IC probably is suffering from an electrostatic discharge. Carpet is no place to troubleshoot circuits. The IC can support 1A at 5V so it's most likely not the heater. Replace the IC, find a bench and possibly an ESD mat with a strap. Then slowly 'ramp' up the load with lower and lower value resistors. 

Another problem that you may be facing is the poor parasitics of the breadboard.
The ESR of the inductor will be much higher with the contact resistance of the breadboard. With many DC to DC designs, the making the traces that are 10's of mills can create problems with a design (milliohms make a difference). 

The resistance on the pins plus the contact resistance is probably causing issues also. If you get this up and running again check the voltage bounce on the ground pin of the regulator before going to full current with an oscilloscope. 

Also the loop will not be properly compensated as there is roughly 20pF of capacitance between rows, this could also cause problems with the compensation which could lead to instability in the feedback loop of the buck converter. 

Don't use a breadboard with DC to DC's, use perfboard and soldering or wirewrapping. Use the PCB layout guidelines (even when soldering)