There is a fault menu on the drive and it does keep a history. Although I am sceptical it's your drive.
Also as vator gator stated the normally closed TH contact is a thermal sensor on the DB resistors. I would like to add there is another item that senses heat that will shut down your elevator. The SPU board has a heat sensitive chip mounted on it.
Are your service calls always come in during peek times of the day? This maybe a bit of a long shot, point a fan at the SPU...
Good luck and please keep us posted.
