McDonnell & Miller 751P-MT-U-120 Control

The McDonnell & Miller 751P-MT-U-120 (Part Number 176214) is a heavy-duty 120Vac manual reset low water cut-off engineered for reliable performance in commercial and industrial hot water and steam boilers. As a veteran-grade electronic boiler safety control, this unit is fully ASME CSD-1 compliant, ensuring the burner remains locked out following a low water event or power interruption until a technician manually initiates the reset. The integrated extended barrel probe (PA-800U) is specifically designed for systems requiring deeper insertion or clearance through thick insulation, providing precise 20,000 ohms sensitivity to detect water levels accurately even in high-temperature environments up to 250°F.

For contractors, the 751P-MT-U-120 Control simplifies troubleshooting with clear LED diagnostic indicators—green for power status and red for low water conditions. The built-in test switch allows for immediate verification of system bypass and relay functionality without draining the header. This probe-type LWCO features a NEMA 1 enclosure and is rated for a maximum steam pressure of 15 psi and water pressure up to 160 psi. Rigorous boiler safety requirements are met through its failsafe logic, preventing dry-fire scenarios by maintaining the cut-off state if power is restored while a low-water condition persists.

• ASME CSD-1 Compliance: Meets strict jurisdictional codes for manual reset secondary protection on steam and primary protection on hot water systems.
• Extended Barrel Probe: The "U" model includes an extended probe length for specialized boiler tappings and high-insulation applications, ensuring PA-800U probe compatibility.
• Enhanced Diagnostics: Dual LED lights and a technician-accessible test switch streamline routine maintenance and system health checks.
• Power Loss Security: Prevents automatic burner restart after power outages if the water level hasn't been safely restored to the electronic sensor.
• Durability: Designed for industrial boiler control with a 160 psi maximum water pressure rating and 250°F temperature threshold.

Is this unit compatible with glycol-treated systems?
Yes, the McDonnell & Miller 176214 is effective in systems with up to a 50% glycol concentration, provided the probe sensitivity remains within the 20,000 ohms threshold.

Can this be used as a primary control on steam boilers?
Per code, manual reset low water cut-offs like the 751P series are typically utilized as secondary protection for steam applications, while serving as primary or secondary controls for hot water boilers.

What is the purpose of the 'U' designation?
The 'U' indicates the inclusion of an extended barrel probe, which is necessary when standard probes cannot reach the water line due to specific boiler manifold or tapping geometries.

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.