The core charging high limit switch is located inside the back panel and extends across the length of the heater. This limit switch monitors temperature between the steel back panel and the insulation panel within the heater and is connected in series with the Clearance Violation Limit Switch to the Limit 1 (L1) and Limit 2 (L2) terminals on the Base IO Board.
The core charging high limit switch is a linear high limit which opens on temperature rise. If normal operating temperatures are exceeded, the limit will open and interrupt power to the heating element relays. The heater's control panel may display "CORE FAIL".
If the "CORE FAIL" message occurs 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 the high limit switch is highly unlikely. If there is continuity (less than 10 ohms) at the leads when the capillary tube is cool and the part is not physically damaged, it can be assumed good.
NOTE: When replacing a high limit switch, DO NOT use water-based lubricant to aid in the installation.
Auto reset and manual reset core charging high limit switches are not interchangeable. The limit switch used as a replacement MUST be the same style and type as the limit switch the heater was manufactured with.
