The core charging high limit switches are located inside the back panel and extend across the length of the heater. This limit switch monitors temperature between the steel back panel and the insulation panel within the heater. If normal operating temperature is exceeded, the limit switches will open and interrupt power to the heating elements. The core charging high limit switch(es) will automatically reset when the temperature returns to a normal range.
If one or both of the limit switches opens repeatedly, verify that the heater clearances have not been violated and that objects have not fallen between the heater and the wall. If clearances are correct, it is possible that the heater is overcharging or the back insulation panel has been damaged. Failure of a core charging high limit switch is highly unlikely. If there is continuity (less than 10 ohms) at the leads where the capillary tube is cool and the part is not physically damaged, it can be assumed good.
In most applications, if the heater's service light is illuminated, the heater is overcharging and will be hot to the touch.
NOTE: When replacing a high limit switch, DO NOT use water-based lubricant to aid in the installation.