| Had the same thing a couple of years back.
Turned out the pushrod wasn't returning far enough in the master cylinder and therefor not releasing the pressure in the calliper. As the pads rubed the disc it heated the system, expanding the fluid therefor applying more and more pressure on the brake. Allowed it to cool and all was back to normal... until the next time!
A twist of the adjuster bolt allowing the rod to return a little further and not had the problem since.
Credit goes to Nelly for finding and resolving that for me. | 
Threaded Mode