FlashForge Creator Pro Tool Failure! Temp limit reached
It sounds like a failed TC amp chip. But we need to rule out some other stuff. 

Some important facts about the Creator Pro temp sensor:


If you smash and short the two thermocouple wires together, the printer will simply read room temp.
If you cut or disconnect the thermocouple wires, the printer will report NC for "not connected."
The thermocouple lookup table in the firmware only goes up to 300C. 


Seeing a number over 300C means either a bad thermocouple amp chip, or excess voltage on the TC wires due to a short to something else in the hot block. (However, such a short will usually fry the entire controller board to smithereens.)

To rule out stray voltage entering the TC wires, completely detach both thermocouples from the hot blocks and lay them out not touching anything metal. Do you still get an unusually high reading on tool 0? 

To rule out an issue with the specific thermocouple, swap thermocouples between tool 0 and tool 1 and see if the problem moves with the TCs.

If the TC is not touching anything, and the problem stays with the tool when you swap wires, and you STILL get >300C reads, the thermocouple amp chip has failed. It is possible to replace the chip if you have (or your friend has) a hot air rework station and some experience soldering. Or you can get a new mainboard from FlashForge. 

The next question is why this problem happened. You don't want to fix the symptoms with new parts but have an underlying issue cause the same failure to re-occur after you swap out parts. With the printer on but the heaters off, use a multimeter to check for voltage between the hot block and the printer's ground. Certain types of heater cartridge failure can short the hot block to +24v. This is highly dangerous and needs to be fixed before you continue using the printer. So make sure you check it before trying to repair anything else.