Could it be some company (hospital in this case) policies need to be tightend up? In our company no one uses a tool on a piece of equipment without first clearing it by me.(head of maintenance). All the employees are aware of this and would not let any outside person work on anything without making sure I approved it. I would certainly re-check the oven before letting it go into service again. It sounds like you did a thourgh job on your initial troubleshooting and repair. No outside person can ever know a piece of equipment like a good maintenance person can that is around it all the time and keeps good up to date records on it. He took the Master key? to what? Sounds like a case for law enforcement officials. 10 amp switch on a 15 amp circuit? Could have been that way from factory. I had a piece of new equipment with a 5 hp motor come to me from the factory once with a switch that was only rated for a 2 hp motor.