Honeywell, 121371B/U, Copper Well Assembly

Honeywell 121371B/U – 3/4" x 3" Copper Aquastat Well with Mounting Clip

The Honeywell 121371B/U is a 3-inch immersion well designed for use with Aquastat temperature controllers. This component provides a reliable thermal interface between the sensing bulb and the controlled medium in hydronic heating systems. It is constructed from copper for efficient heat conduction and corrosion resistance and includes a mounting clamp for secure sensor positioning.

The 3/4" NPT thread allows direct insertion into standard boiler tappings, while the 3-inch well length supports standard bulb sizes for accurate control and limit applications. This well is commonly used in residential and commercial boiler systems for temperature regulation and safety cutout functions.

Product Features

• Material: Copper body for efficient thermal response and resistance to corrosion
• Well Length: 3 inches insertion depth, suitable for standard 3/8" x 2-7/8" sensing bulbs
• Thread Size: 3/4 inch NPT for standard hydronic tapping compatibility
• Insulation Depth: 1-1/2 inches
• Mounting: Includes clip to hold bulb in proper position within the well

Technical Specifications

• Compatible Bulb Size: 3/8" diameter x 2-7/8" length
• Insertion Depth: 3 inches
• Thread Type: 3/4" NPT
• Material: Copper
• Includes: Bulb clip/mounting spring

Installation Notes

This well should be installed by a licensed HVAC or plumbing professional. It must be properly threaded into the boiler tapping using approved sealing compounds or thread tape, and fully tightened to ensure leak-free operation. Verify full bulb insertion and secure attachment using the included mounting clip to maintain accurate sensing performance.

Application

• Used with immersion-type Aquastat controllers
• Applicable for hot water boilers, storage tanks, and process piping
• Supports temperature control and limit functions in hydronic systems