Furnace Not Heating Due to Tripped High-Limit Switch

The high-limit switch is a safety sensor that shuts down the heating elements when internal temperatures exceed safe operating parameters. To confirm this is the cause, inspect the air filter for heavy accumulation of dust or debris. Then, use a multimeter set to continuity (Ω) to test the switch terminals while the unit is cool. If the meter displays an open loop (infinite resistance) while the system is cool, the switch has tripped or failed internally, preventing the furnace from restarting.

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