I've been using a beta version of Cura designed specifically for the BCN Sigma machine and, just in normal Cura, for some reason there is no click box that specifies you just want to use the second extruder. My first extruder is having issues so I wanted to print with the second.
I'm new to this stuff, but I took a look at my G-Code and saw that there was no T0 or T1 anywhere. I found that really confusing but figured that T0 was the default setting, somewhere, anyway. I tried just popping in T1 in the M109 S215 line but that didn't work - T0 still came out to print... It seems that after the G92 command (all listed above in previous posts) the Sigma reverts to using T0 anyway. The result was that T1 was hot and extruding in preparation for printing, but then T0 was going out and trying to print cold anyway.
My solution was just to rewrite T1 underneath the M117 Printing message. That fixed it and I'm now printing happily using the second non-faulty extruder. BCN have massive firmware issues at the moment so USB printing is out of action and I'm using an SD card - viewing the G-Code in Notepad and editing it there. Is that best? Usually I print using a USB IoT device and slice using Formide, which does have the option to select which extruder you want to use. Why doesn't Cura have this? It seems they removed it before February 2015, judging from other forums on similar issues (not Sigma-beta).
So, in summary for others with issues, just write T1 at the end of the Start G-Code if you want to print using the other extruder. Otherwise the printer reverts to the default T0. Perhaps this applies to normal non-BCN-beta slicing too.
Anybody know why this is?