McDonnell & Miller RB-122E Control

The McDonnell & Miller RB-122E (Part Number 144676) is a heavy-duty conductance-type low water cut-off designed specifically for residential and light commercial hot water boilers. As a veteran-preferred electronic LWCO, it features a 120VAC power requirement and a 3/4" NPT connection, making it high-performance protection against dry firing. This unit includes a patented self-cleaning probe that reduces scale build-up—a common failure point in hydronic systems—and extends your maintenance intervals. The automatic reset functionality ensures the system resumes operation immediately once water levels are restored, while the integrated test switch allows contractors to verify burner circuit interruption without draining the loop. Rated for a maximum water pressure of 160 psi and a maximum water temperature of 250°F, the RB-122E provides the reliability needed for modern high-efficiency boiler installations. The compact design and probe-style mounting simplify installation in small riser pipes or boiler tapping ports where space is at a premium.

• Self-Cleaning Probe: Patented technology minimizes mineral and scale accumulation on the sensor tip to prevent false low water cut-off triggers.
• Contractor-Friendly Testing: Built-in test button enables quick verification of the control circuit and burner shutdown without manual water level manipulation.
• Fail-Safe Operation: Automatic reset logic ensures heat restoration immediately after a water loss or power event is resolved.
• High Temperature Resilience: Designed to handle hot water boiler environments up to 250°F and 160 psi.
• Diagnostic Indicators: Dual LED lights provide instant status updates for "Power On" (Green) and "Low Water" (Red).

Can I use this on a steam boiler?
No, the RB-122E is specifically engineered for hot water boilers. Steam applications require different float-style or probe-style controls designed for surging water lines.

Does this unit require a blow-down valve?
Because this is a probe-type electronic LWCO for hot water, manual blow-down is not required, significantly reducing routine maintenance for the end-user.

Can it be installed in any orientation?
The probe must be installed horizontally or vertically in a riser pipe or boiler tapping, ensuring it is above the minimum safe water level as specified by the boiler manufacturer.

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.