Description
The Lennox 73K21 is an OEM auto-reset limit switch engineered to protect furnaces and heating systems from dangerous overtemperature conditions. When supply-air or heat exchanger temperatures exceed the rated cutout threshold, the switch opens the control circuit — shutting down the burner — and automatically resets once temperatures return to a safe operating range, eliminating the need for manual intervention during normal cycling.
How It Works
The limit switch continuously monitors air temperature within the furnace plenum or heat exchanger area. If the sensed temperature rises to the cutout point, the switch opens, interrupting the burner control circuit and preventing heat exchanger damage, component failure, or fire hazard. The automatic (AUTO) reset function closes the circuit again once the temperature drops back to a safe level, restoring normal operation without requiring a service call for routine thermal events.
Key Specifications
- Brand: Lennox
- Part Number / SKU: 73K21
- Switch Type: Auto-Reset (AUTO)
- Temperature Set Point: 145°F
- Temperature Cutout: 175°F
- OEM Replacement for Lennox heating systems
Features & Benefits
- Auto-reset design restores operation automatically after cool-down — no manual reset required
- Protects heat exchangers, burners, and downstream components from overtemperature damage
- Direct OEM Lennox replacement ensures proper fit, function, and reliability
- Helps maintain system efficiency by quickly cycling the burner back on after a safe temperature is reached
- Essential safety component for residential and light-commercial Lennox furnace applications
Application
Designed as a direct OEM replacement for compatible Lennox furnaces. Always verify compatibility with your specific model number before installation. Installation should be performed by a qualified HVAC technician in accordance with local codes and the equipment manufacturer’s guidelines.
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