The surface temperature, for safety reasons, is limited to appoximately 203ºF / 95 °C.  The device automatically starts again after a cooling down to under 113º F, or 45°C.
According to the manufacturer:
The limiter switch off at 140°C. Half of the limiters are mounted in the upper third, half in the lower third, when panel is mounted horizontally.
LAVA  | 
number of Limiters  | 
250=  | 
6  | 
500=  | 
6  | 
750=  | 
8  | 
1000=  | 
 10  |