Background Info: For whatever reason, a certain version of Inventor Firmware (inventorII- - 复件, specifically) doesn't allow the hotend/nozzle to begin heating up. This was confirmed on test printers we had in our shop that exhibited the issue. At first we thought it was a bad heater cartridge and left the printers idle until we could get replacements. For other testing, we swapped the mainboard/motherboard in the back of the printer, that controls everything. The new (swapped in) motherboard allowed the printer to heat up normally. SO - we assumed a bad board is what keeps the printer from heating up. So, we updated the firmware on that board to the Polar Cloud Compatible firmware from 04.09.2018. The printer was put on the shelf for more testing and printing. Oddly enough, the printer wouldn't heat up. We reversed the firmware back to an earlier version and, again, it was able to heat up. The 04.09.2018 version of the firmware affects only some printers and keeps them from heating up, while all other features work normally.

Fix: update to the 04.25.2018 firmware at this link, using these instructions (ignore the alpha/beta and versioning).