Aquastat Hi/Lo Limit Controller | Replaces Honeywell L6006C1018/U | NBK-21189

NBK-21189 – Aquastat Hi/Lo Limit Controller | Replaces Honeywell L6006C1018/U

The NBK-21189 Aquastat Hi/Lo Limit Controller is a precision temperature control device engineered for hydronic heating systems, outdoor wood boilers, and hot water heating applications. With dual high- and low-temperature setpoints, it automatically protects your system from overheating and maintains safe, efficient operation — giving you peace of mind season after season.

Key Features

• Dual Hi/Lo Setpoints – Independently adjustable high and low temperature thresholds for precise system control
• Automatic Safety Shutoff – Cuts burner or circulator operation the moment temperature limits are exceeded
• Adjustable Differential – Fine-tune cycle characteristics to maximize system efficiency and reduce short-cycling
• Versatile Compatibility – Suitable for outdoor wood boilers, hydronic baseboard, and radiant heating systems
• Direct OEM Replacement – Drop-in replacement for Honeywell L6006C1018/U with no modifications required

Specifications

• SKU: NBK-21189
• Part Number: 21189-NBK
• Type: Aquastat Hi/Lo Limit Controller
• Application: Outdoor wood boilers, hydronic heating, hot water heating systems

Replaces / Cross-Reference

• Honeywell: L6006C1018/U

Common Applications

• Outdoor wood boilers and biomass boilers
• Hydronic baseboard and radiant floor heating systems
• Hot water storage tanks requiring dependable high/low limit control

Why Choose the NBK-21189?

When your heating system needs reliable temperature protection, the NBK-21189 delivers. Its dual-setpoint design and automatic shutoff safeguard your boiler and circulator from thermal damage, while the adjustable differential keeps your system running at peak efficiency. A trusted, cost-effective replacement for Honeywell L6006C1018/U.