McDonnell & Miller 750-MT-24 Control

The McDonnell & Miller 750-MT-24 (Part Number 176293) is a heavy-duty 24Vac manual reset low water cut off designed for professional integration into both hot water and steam boilers. As a veteran-grade electronic LWCO, this unit serves as a reliable primary or secondary control for commercial and industrial hydronic systems. This GuardDog Series 750 control features a manual reset mechanism, ensuring that once a low water condition is detected and the burner is tripped, the system remains locked out until an on-site technician verifies the water level and manually clears the fault. This logic is critical for ASME Standard CSD-1 compliance, providing a necessary failsafe for high-output boiler configurations.

Engineered for durability in demanding mechanical rooms, the 750-MT-24 utilizes conductance-actuated technology with a 20,000 ohms sensitivity probe. The integrated test switch allows contractors to verify circuit integrity without draining the entire system, while the clear LED interface provides instant diagnostic feedback: a green LED for power status and a red LED for low water alerts. Designed for direct mounting into 3/4" NPT boiler tappings, this 24V boiler safety control offers robust protection against dry-fire conditions in both low-pressure steam and high-temperature hot water applications.

• CSD-1 Compliant Safeties: The manual reset functionality meets strict code requirements for secondary monitoring on steam and hot water systems.
• Integrated Diagnostics: Features an accessible test switch and dual LED indicators (Green for Power, Red for Low Water) for rapid troubleshooting.
• Universal 24V Compatibility: Standard 24Vac operation integrates seamlessly with most contemporary boiler burner control circuits.
• Reliable Probe Sensitivity: Calibrated to 20,000 ohms to maintain stable operation across diverse water qualities and temperatures up to 250°F.
• No Nuisance Lockouts: Internal logic prevents lockouts during temporary power interruptions if the probe remains submerged.

How do I reset the 750-MT-24 after a low water event?
Once the water level is restored above the probe, you must manually depress the reset button on the housing. The LED indicators will flash to signal the circuit has been re-energized.

Can this be used as a primary LWCO on steam boilers?
According to standard HVACR safety protocols, manual reset models like the 176293 are typically utilized as a secondary control on steam systems, whereas they can serve as either primary or secondary on hot water boilers.

What is the maximum pressure rating for this control?
This unit is rated for a maximum water pressure of 160 psi and a maximum steam pressure of 15 psi, making it suitable for most low-pressure commercial applications.

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.