Honeywell 550p Low Water Cut-off 120V Commercial Boiler

Product Description

The HONEYWELL 550p is a low water cut-off (LWCO) control designed for commercial water boilers operating at 120 volts. The unit monitors boiler water level and interrupts burner operation when water drops below a safe threshold, protecting the heat exchanger and pressure vessel from dry-fire damage. It includes a manual reset function, requiring a deliberate technician action before the burner can restart after a low-water lockout. The 550p ships with the EL1214-P probe, giving the installer a complete sensing assembly out of the box. This control is installed and serviced by licensed plumbers, pipefitters, and boiler technicians.

The 550p is suited for commercial hydronic heating systems where low-water protection is a code-required safety function. Manual reset is the appropriate choice in commercial settings because it prevents automatic burner restart after a safety trip, ensuring a technician inspects the system before returning it to service. Typical installation locations include packaged commercial water boilers, large cast-iron sectional boilers, and similar 120-volt hot-water heating equipment. This control replaces 29000, OEM170MC, MM 900M, and PS851M-120.

Key Features

• Low water cut-off function shuts down burner when water level drops below the probe setpoint
• Manual reset prevents automatic restart after a low-water lockout event
• Operates at 120 volts for compatibility with standard commercial boiler control circuits
• Includes EL1214-P probe — complete sensing assembly included, no separate probe purchase required
• Direct replacement for multiple legacy part numbers including 29000, OEM170MC, MM 900M, and PS851M-120

Compatibility

The 550p is a direct replacement for part numbers 29000, OEM170MC, MM 900M, and PS851M-120 on commercial water boilers. It is designed for 120-volt commercial hot-water boiler applications.

Installation Notes

Installation must be performed by a licensed boiler technician, plumber, or pipefitter in accordance with local mechanical codes and the boiler manufacturer's instructions. Shut off power to the boiler control circuit and allow the system to cool and depressurize before removing the existing control or probe. After mounting the 550p and installing the EL1214-P probe, verify the probe penetrates the boiler vessel at the correct water-level port per the boiler manufacturer's specification. Following installation, perform a manual low-water test by dropping water level below the probe to confirm lockout and manual reset function before returning the boiler to service.

Technical Specifications

• Voltage: 120 volts
• Function: Low water cut-off with manual reset
• Application: Commercial water boiler
• Included Components: EL1214-P probe
• Replaces: 29000, OEM170MC, MM 900M, PS851M-120

Standard Information

• Brand: HONEYWELL
• Manufacturer Part Number: 550p