After opening the iPad, i found that it had been opened before. I could tell as the logic board had missing screws, the battery has been replaced before, some plastic parts were missing and the external keyboard connector was severely bent. After further disassembling the iPad, i noticed that the battery connector on the logic board had a pin missing as outlined in this image from the iFixit repair manual:
[image|3570708]
I think the previous “repair” guy wasn’t careful enough and had broken the pin that was used to monitor the TG0B thermal sensor.