High or Low Limit Remote Bulb Aquastat, 100-240-Degree (F), 5-30-Degree (F) Adj Differential, L4008A1015

The Resideo L4008A1015 is a remote bulb aquastat designed for limiting or regulating liquid temperature in boilers, tanks, and hydronic systems. With a sensing range of 100°F to 240°F and an adjustable differential of 5°F to 30°F, this controller provides precise temperature management where you need it. The 66-inch capillary tube allows the remote sensing element to be mounted directly into the boiler or tank, while the control box mounts separately on a vertical surface for easy adjustment and visibility. Built with a totally enclosed Micro Switch snap-acting switch rated for 8A at 120 Vac or 5.1A at 240 Vac, this aquastat delivers reliable high or low limit control in residential and light commercial heating applications.

• 100-240°F Temperature Range: The L4008A1015 operates across a 100°F to 240°F sensing range, covering the full spectrum of typical boiler and indirect tank operating temperatures. This wide range lets you set the exact high or low limit your system requires without needing multiple controls.

• 5-30°F Adjustable Differential: The differential (the temperature swing between when contacts close and when they open) adjusts from 5°F to 30°F via an external screw. A tighter differential means more frequent cycling and tighter temperature control, while a wider differential reduces boiler short-cycling and improves efficiency in systems where precise temperature isn't critical.

• 66-Inch Capillary with Remote Bulb: The 3/8-inch by 2-7/8-inch sensing bulb connects to the control via a 66-inch (5.5-foot) capillary tube. This remote sensing design lets you mount the bulb directly in the liquid (horizontally or vertically) while keeping the control box accessible on a wall, so you can read the scale and adjust settings without reaching into tight mechanical spaces.

• Totally Enclosed Micro Switch: The snap-acting switch inside the L4008A1015 is fully enclosed, protecting contacts from moisture, dust, and debris. This design extends switch life and maintains reliable operation in boiler rooms and mechanical spaces where humidity and particulates are common.

• Visible Scale and External Adjustment: The control point scale is printed on the front of the case, and the adjustment screw is accessible from outside. You can verify and change the setpoint without opening the enclosure, making commissioning and seasonal adjustments faster.

• High and Low Limit Applications: This single control functions as either a high limit safety (breaking the circuit when temperature rises too high) or a low limit operating control (closing the circuit to call for heat when temperature drops). The SPST contacts break on temperature rise, so wiring determines whether it acts as a safety cutout or an operating controller.

• UL and CSA Certified: The L4008A1015 carries UL Component Recognition (File No. MP466, Vol. 6, Sec.1, Guide No. MBPR2) and is CSA Certified (File No. LR95329-1), meeting North American electrical and safety standards for installation in boiler and hydronic heating systems.

The L4008A1015 works with any boiler, indirect water heater, or storage tank system that requires remote bulb temperature sensing within the 100-240°F range. It can control line voltage burners, circulators, or zone valves directly at 8A @ 120 Vac or 5.1A @ 240 Vac, and can also switch low-voltage (0.25 A @ 0.25 to 12 Vdc) circuits for interfacing with relay or zone control panels. The sensing bulb mounts horizontally or vertically into a boiler tapping, immersion well, or tank sensor port. The control case mounts to any vertical surface in ambient temperatures up to 150°F. No separate well is included; you must supply a compatible immersion well or direct-mount the bulb per your system's requirements.

Mount the sensing bulb so it's fully immersed in the liquid and bottoms out in the well or tapping to ensure accurate temperature reading. The control case mounts on a vertical wall or panel using the screw holes in the back. Make electrical connections to the quick-connect terminals inside the case, following the wiring diagram in the installation instructions. Once installed, set the temperature setpoint and differential using the external adjustment screws and the visible scale. The L4008A1015 requires no routine maintenance; the sealed switch and remote bulb design eliminate the need for periodic cleaning or lubrication.

• L4008A1015 aquastat controller with remote sensing bulb and 66-inch capillary tube

A: The Resideo L4008A1015 installation instructions are available as a PDF download from the product page. The manual covers mounting the sensing bulb, wiring the control for high or low limit operation, setting the temperature and differential, and electrical specifications. You'll find wiring diagrams, terminal identification, and step-by-step setup procedures to ensure correct installation and safe operation.

A: The L4008A1015 uses quick-connect terminals inside the case for line and load connections. For high limit safety operation, wire so that the normally closed contacts are in series with the burner circuit; when temperature rises past the setpoint, contacts open and shut off the burner. For low limit operating control, wire so contacts close on temperature drop to call a boiler or pump. The installation instructions include wiring diagrams for both configurations. Always follow local electrical codes and turn off power before making connections.