Marley Engineered Products 4520-2018-003 Limit Switch

The Marley Engineered Products 4520-2018-003 Limit Switch is a critical safety component engineered for forced-air heating applications where precise thermal protection is non-negotiable. This 180 degree F auto reset limit switch serves as a high-limit safety cut-out, functioning as a normally closed (NC) switch that opens the circuit if the plenum or heating element temperature exceeds the 180°F threshold. As a genuine Marley OEM replacement part, it ensures exact fitment and calibration for Berko and QMark electric heaters, preventing thermal runaway and protecting the heat exchanger from damage. This HVAC high limit sensor features an automatic reset mechanism, allowing the heater to resume operation once ambient temperatures drop below the differential setpoint. Maintaining system safety controls with high-quality induction-hardened components is vital for reducing nuisance trips and ensuring long-term duty cycle reliability in commercial and industrial environments.

Key Benefits for Technicians

• OEM Precision: Guaranteed compatibility with Berko and QMark units, eliminating the risks associated with generic thermal overload switches.
• Automatic Restoration: The 180°F auto reset functionality reduces the need for manual site visits to reset tripped units after temporary airflow obstructions.
• Critical Safety: Acts as a primary hi-limit safety control to interrupt power to the heating element when dangerous temperatures are detected.
• Application Versatility: Suitable for use in a variety of forced air heating systems requiring a fixed-temperature cutout.

Common Questions

What causes this limit switch to trip frequently?
Frequent tripping usually indicates restricted airflow, such as a clogged filter, a failing blower motor, or obstructed return air vents, causing the Marley 4520-2018-003 to reach its 180°F trip point.

Can this be used as a manual reset switch?
No, this is an auto reset thermal switch. If your specific heater wiring schematic requires a manual reset for safety compliance, this component should not be substituted.

Is the 180 degree F rating adjustable?
This is a fixed-temperature high limit safety device. The 180°F setpoint is factory-calibrated and cannot be adjusted in the field to ensure operational integrity.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.