High Limit Thermostat, SAFETY LIMIT
THERMOSTAT,  80-100deg C

When the limit temperature is reached on rising medium temperature, contact changes over to contact (alarm) and the limiter remains tripped in this position.
When the temperature of the medium falls by the value of the switching differential, the  safety limiter must be manually reset after removal of the threaded nipple.
Should the expansion liquid escape through a leak in the sensing system, the pressure in the diaphragm drops, causing the contact connection to mechanically 11-12 off.