Electronic Low Water Cut-Off, 24V

McDonnell & Miller RB-24E – Electronic Low Water Cut-Off for Residential Gas Boilers

The McDonnell & Miller RB-24E is a 24V electronic low water cut-off designed to provide critical boiler protection by shutting down burner operation when unsafe water levels are detected. Built for residential gas-fired hot water boilers, this unit combines precision water sensing with a compact, installer-friendly design that supports both retrofit and new installations.

Reliable Boiler Safety with Minimal Maintenance

This model features a solid-state control module with an integrated LED status system and self-cleaning probe, reducing false trips caused by scale buildup. With universal plug-and-play wiring and brass-threaded connections, the RB-24E ensures a tight seal and simplified installation on standard ¾" NPT tappings.

Performance Highlights

• Self-Cleaning Probe – Minimizes scale accumulation and extends maintenance intervals to up to 5 years under normal water conditions.
• Automatic Reset – Control resumes operation once normal water level is restored, reducing nuisance service calls.
• LED Status Indicators – Red light signals low water shutdown; green indicates power on and system ready.
• Universal Wiring Harness – Pre-wired plug simplifies field installation across a variety of boiler brands.
• Compact Housing – Designed to fit tight clearance areas common in residential mechanical rooms.

Technical Specifications

• Voltage: 24 VAC
• Switch Capacity: 2 amps resistive load
• Connection Size: 3/4" NPT
• Probe Sensitivity: 15,000 Ohms
• Max Working Pressure: 160 PSI
• Water Temperature Limit: 250°F (121°C)
• Ambient Temperature Limit: 120°F (49°C)
• Dimensions: 5-3/4" L x 1-7/8" W

Installation Guidance

The RB-24E is optimized for quick setup using its integrated wrench flats and brass threads for a secure fit. While the wiring harness supports plug-and-play installation, the control should be installed and tested by a licensed HVAC or plumbing contractor to ensure code compliance and proper burner interlock integration.

Contractor Applications

This low water cut-off is ideal for residential gas boiler systems where compact footprint, safety compliance, and serviceability matter. It is a smart choice for boiler upgrades or for meeting jurisdictional requirements in municipalities mandating electronic water level control.

Field-Proven Protection

The McDonnell & Miller RB-24E offers reliable shutoff control and simplified diagnostics in a compact design. From routine service to emergency replacements, this unit delivers long-term protection and efficiency—helping contractors prevent dry-firing and preserve boiler performance year-round.