Troubleshoot Seventeen Faulty Vape Devices

My collection of personal vapour devices has gradually stopped performing: the LED still lights up, yet no vapour is produced. I have already swapped in fresh batteries, brand-new coils/atomizers, and even replacement circuit boards, so the usual quick fixes are exhausted... (Budget: $30 - $250 USD, Jobs: Circuit Design, Electrical Engineering, Electronics, PCB Design and Layout, Schematic Review, Technical Support, Troubleshooting)