I have a ZZ machine with very similar lines, I think I posted it earlier in this thread. It's my American Home machine.
I also have several of those foot controllers. They are one of my favorite designs. Very comfortable and responsive. MUCH better than the little button one Singer made for so long.
The heating comes from the resistance unit doing it's job. When you run the machine fast the resistance is low to allow full voltage to the motor. When you run it slow the resistance is high to reduce the voltage. The voltage has to go somewhere so it's turned into heat by the wire coils around the ceramic block and dissipated.
You have a PM on the way.