Honeywell L6006A Aquastat controller Honeywell L6006A Aquastat Information
Buy, replace, install, set-up, & wire the L6006A aquastat control

  • AQUASTAT L6006A HONEYWELL GUIDE - CONTENTS: Guide to the functions of the Honeywell L6006A heating boiler combination control aquasta, L6006A aquastat iInstallation manuals. Guide to the Honeywell 6006 Single Function Boiler Limit Control, How to set the HI LO and DIFF on a heating boiler control.
  • POST a QUESTION or READ FAQs about Aquastats controls used on Heating Boilers

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Guide to aquastat controls on heating equipment:

This article series explains how aquastats work and what the different aquastat controls are, what they do, and how they are set. We define the HI LO and DIFF controls on heating boiler aquastats and explains what they do and how they work. We explain the location and use of the heating boiler reset button found on aquastats.

We discuss relationship among HI, LO, DIFF, and heating burner cut-in, cut-out, and circulator lockout that are provided on the combination control. We explain how the Aquastat controls hot water production via a tankless coil on the heating boiler.

We explain how to disable the LO control when a tankless coil is not in use on a boiler. After explaining the operation of an aquastat's Hi, Lo, and Diff controls we review the newer universal replacement aquastat from Honeywell, the L7224U Universal Aquastat, followed by a discussion of the simpler single-limit control switches.

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Honeywell L6006A Aquastat Settings & Controls

Honeywell L6006A Aquastat controller

Reader Question: how to set the large and small dials on the Honeywell L6006A

(Dec 23, 2014) Mark said:
I was looking for a bit more explanation (or perhaps just a layman's explanation) of an aquastat's hi/low/diff functions as it relates to my specific situation.

[Click to enlarge any image]

My aquastat is the Honeywell L6006A. It has one large dial and one smaller (differential) dial. It is attached downstream from a heat exchanger/air handler unit in my gas-fired hydronic heating system, and the fan is being controlled by the aquastat.

I have the large dial at 160and the differential to 5 degrees.

Does this mean that when the water in the heat exchanger reaches approx 165 the fan should turn-on, and when it cools to approx 155 it should turn-off?


Thanks Mark:

The large dial whose numbers you see when the control cover is on is the HI or HIGH LIMIT - see SETPOINT INDICATING WHEELin Honeywell's illustration adapted at above left

There is a smaller DIFFerential setting dial inside the control - in the illustration at above left see DIFFERENTIAL ADJUSTMENT WHEEL.

The aquastat is monitoring water temperature at the point where its sensor is installed in order to turn the burner on and off.

Click and enlarge the white, green, yellow illustration in the article just above to see how a typical Honeywell control relates the DIFF setting to heat on or off.

Here is what the manufacturer says:

Key is this phrase about the High Limit found below:

Turns on burner at temperature setting, minus differential.

For proper selection of settings, follow the boiler manufacturer recommendations.

Watch out: although it may be marked as "optionl" in some company illustrations, the company also provides and recommends use of a heat-conducting grease when installing the L606A high limit controller into its immersion well on the heating appliance. Without good thermal contact between the temperature sensing bulb [ INSERTION ELEMENT in the illustration above and shown in detail just below] the control may not operate reliably.

Aquastat immersion well  sensor details, adapted from Honeywell's L7224U universal aquastat installation instructions cited in this article series (C) InspectApedia 2015

[Click to enlarge any image]

Honeywell L6006A High limit controller

— Shuts off burner when water temperature exceeds high limit setting. Burner restarts when temperature drops to high limit setting, less differential.

Honeywell L6006A Low limit controller

— Maintains minimum boiler temperature for domestic hot water. Turns on burner at temperature setting, minus differential.

Honeywell L6006A Circulator controller

— Prevents circulation of water that is not hot enough. Breaks circulator circuit at temperature setting minus differential; remakes the circuit when the temperature setting is reached.

Honeywell L6006A Switching action is as follows:

Upon a drop in boiler water temperature (to dial setting, less differential), makes R to B burner contact; breaks R to W contact, preventing circulator operation.

Upon a rise in boiler water temperature (to dial setting), breaks R to B burner contact, makes R to W circulator contact

Honeywell L6006A Installation, Wiring & Operation Manual


Continue reading at AQUASTAT HI LO DIFF SETTINGS that explains the best settings to use & how & when to disable the LOW & DIFF controls or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AQUASTAT L6006A, HONEYWELL [PDF] for installation & wiring details

Or see MANUALS for HEATING SYSTEM CONTROLS for a list of aquastat installation & repair guides

Or see this

Article Series Contents

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