McDonnell & Miller RB-24E-A Wiring Harness

The McDonnell & Miller RB-24E-A (Part Number 144694) is a heavy-duty 24Vac low water cut-off designed specifically for residential hot water boilers. Featuring a 3/4" NPT connection with brass threads for a high-integrity metal-to-metal seat, this conductance-type LWCO ensures dependable dry-fire protection. The integrated vent damper wiring harness simplifies the circuit, allowing for a clean "plug and play" interface with most modern gas-fired systems. Using solid-state operation and a self-cleaning probe with 15,000 ohms sensitivity, it accurately monitors the presence of water to prevent catastrophic boiler damage. The unit includes a manual test switch for routine diagnostic checks and an automatic reset function that resumes burner operation immediately once safe water levels are restored after a power outage. With its compact design and green/red LED status indicators, it is an essential safety control for any professional hydronic heating system installation.

Key Benefits

• Universal Compatibility: The vent damper wiring harness is designed to fit nearly 100% of today's residential gas boilers, streamlining field replacements.
• Durable Construction: Heavy-duty brass threads ensure a secure, leak-free connection without the need for Teflon tape, which can interfere with probe conductance.
• Diagnostic Feedback: Features a built-in manual test button and dual LED indicators to quickly verify power on and low water conditions.
• Reliable Safety: The automatic reset residential logic eliminates manual intervention after temporary power loss, provided water levels are at the probe.

Common Questions

Is this harness compatible with older Boilers?
Yes, the McDonnell & Miller 144694 is designed as a universal solution for 24V residential systems, specifically those utilizing an external vent damper circuit.

Can I use Teflon tape on the NPT threads?
No. For a conductance-type LWCO like the RB-24E-A, the probe relies on a metal-to-metal ground. Always use a high-quality pipe sealant instead of tape to maintain electrical continuity.

Does this unit require manual resetting after a low water event?
This model features an auto reset mechanism. Once the water level reaches the 3/4" NPT probe again, the control will automatically close the burner circuit to restore heat.

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.