McDonnell & Miller 750-HW-MT-120 Control

The McDonnell & Miller 750-HW-MT-120 (Part Number 176236) is a heavy-duty 120Vac high water cut-off designed to provide failsafe protection for steam boilers and hot water heating systems. Engineered for commercial and industrial environments, this manual reset control prevents hazardous overfill conditions by interrupting the burner circuit or water feeder pumps the moment water levels exceed the safety probe's threshold. Unlike automatic reset models, the manual reset functionality ensures a technician investigates the cause of the high water event, meeting ASME Standard CSD-1 requirements for secondary safety controls. This electronic water level control features a 20,000 ohms sensitivity and a NEMA 1 enclosure, maintaining reliable conductance signal processing even in high-pressure applications up to 250 psi. With an integrated test switch and visible LED indicators—green for power and red for high water—this unit simplifies routine boiler maintenance and diagnostics for contractors managing complex hydronic systems.

• ASME CSD-1 Compliance: Meets strict regulatory standards for secondary manual reset safety controls on steam and hot water boilers.
• Diagnostic LEDs: Features a green "Power On" light and a red "High Water" light for instant status identification under the hood.
• Fail-Safe Logic: Designed with no lock-out during power loss if the probe remains in water, ensuring the system remains protected upon power restoration.
• Versatile Wiring: Can be configured as a primary or secondary control to shut down burners, deactivate water feeders, or trigger external alarm horns.
• Integrated Testing: Built-in test switch allows technicians to verify internal relay operation and circuit integrity without draining the system.

• Does this unit reset automatically after water levels drop? No, the 750-HW-MT-120 is a manual reset high water cut-off, requiring a physical button press once water levels are below the probe to resume operation.
• What is the maximum pressure rating for this control? When paired with the correct remote sensor, it is rated for a maximum pressure of 250 psi for both steam and water applications.
• Can this be used for low water cut-off? This specific model (176236) is calibrated and intended for high water cut-off applications to prevent boiler flooding.

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.