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Honeywell R8182D control explainedHeating Boiler Aquastat Selection
How to select the right boiler aquastat control

Guide to aquastat control selection for heating boilers or water heaters:

How to figure out which aquastat controller your heating boiler or water heater wants and needs.

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.

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Aquastat Selection Guides

Honeywell L8148 Aquastat description (C) InspectApedia.com The photo at page top shows a Honeywell R8182D combination heating control, also called an "aquastat". Shown in in our illustration here is the Honeywell L8148 Aquastat. So what's the difference among the many types of aquastats used on heating boilers and water heaters or calorifiers or geysers and how do we know which aquastat should be installed?

[Click to enlarge any image]

Question: how do I know which aquastat controller to use on my heater

Iva said:

How do I know if the aquastat controller is the right one for my oil burner furnance.

Reply:

Let's start by being sure we're talking about the same type of heating equipment, Iva. I call forced air or warm air heating systems "furnaces", hot water heating systems "boilers" or "hydronic heating systems", and steam heating systems or "steam boilers".

If you're not sure what kind of heat you have,

see HEATING SYSTEM TYPES.

That out of the way, aquastats are controllers used on hot water or hydronic heating system boilers to control the boiler's heating burner by turning it on or off in response to the boiler temperature, and often to also switch a heating zone circulator pump on or off. Aquastats also may have additional controls and features as I'll describe below.

Features & Properties of a Heating Boiler Aquastat

Basic aquastat features are few and simple:

An aquastat just has a few basic functions to perform: control the high limit that will turn on and off the burner in a response to a call for heat, and to keep heat in the boiler to support a tankless coil if one is installed.

If your boiler doesn't use a tankless coil then you don't need those features, so you would either choose a simpler aquastat without support for a coil or you'd choose one that has those features but turn the features off in the control.

Aquastat models vary by physical orientation

Some confusion among aquastat models has to do with the need to physically fit the aquastat in position on the boiler where other pipes and controls may be in its way. So the same aquastat might be sold designed to be mounted with its rectangular body oriented vertically versus horizontally.

Aquastats vary by using a temperature sensor integral with the aquastat versus a temperature sensor at the end of a flexible coil

Honeywell L8148 Aquastat description (C) InspectApedia.com

Most aquastats mount directly to the body of the boiler, with a temperature sensor on the back of the aquastat designed to insert into a temperature sensor well on the boiler (along with some heat conductive grease). You can see that type of aquastat by looking at the back of the Honeywell L8148 aquastat shown just above.

Other aquastats may have a temperature sensor fixed directly to the aquastat back - shown below using a White Rodgers Aquastat #1131-102 produced by Emerson Controls - White Rodgers whose website, unlike their competitor Honeywell, make it almost impossible to find a chart or table listing all of the company's boiler and water heater controls: they prefer that you give White Rodgers/Emerson a call.

White Rodgers Aquastat selection guide (C) InspectApedia.com

But if there is not enough room around the temperature sensing well on a particular boiler, then an aquastat might mount somewhere nearby while its temperature probe is at the end of a flexible coil of tubing so that the sensor itself can be inserted into the sensor well.

Honeywell L4008 Aquastat controller (C) InspectApedia.com

Use a Universal Replacement Aquastat to Simplify Control Selection

1. To simplify aquastat replacement across a very wide range of boilers, manufacturers like Honeywell make a "universal"replacement unit.

If you choose a universal type aquastat to put on your heating boiler then you're pretty safe that the device can be made to work correctly for your needs.

That's because the specific features that need to be tailored, such as a presence or absence of a tankless coil for domestic hot water, or the actual temperature settings, can be set or chosen using the universal aquastats built-in features.

2. Typically the installation manual for your boiler will specify what type of controller it needs.

3. The manufacturers of aquastats also include or provide a substitution chart so that if you are replacing an existing control that is no longer sold you can find a model that replaces it.

So How do I Choose an Aquastat - "which aquastat do I need" ?

I agree that the number of aquastat controller models can be overwhelming; one needs to consult both the boiler manufacturer and the aquastat manufacturer to see what heating boiler features need to be controlled by the aquastat, what sort of burner and burner electrical wiring need to be controlled by the aquastat, the placement of the aquastat's temperature sensing device, and also the physical mounting space for the aquastat.

If you Do Know the Brand & Model of Aquastat that you are Replacing Use One of These Cross Reference Charts

Then use a manufacturer's aquastat cross reference or replacement chart or select a universal replacement aquastat model.

If you Don't Know the Previous Aquastat Brand & Model Find the Controller Features Your Heater Needs

Basically, if you do not know the brand and model of the aquastat that you are replacing, then you choose an Aquastat by finding or specifying both boiler features and physical installation space for your specific boiler - which is why I said start with the boiler's installation manual.

Examples of Features on Aquastats

Multi-purpose aquastats are controls that manage both heating boiler on and off temperatures or maintenance temperatures and also other features or services. Here are things you'll consider when choosing an aquastat of this type:

Here is an example of aquastat sub-models and their differences using the Honeywell L6006 and L6007 Aquastat Controller as a model:

These Aquastat® Controllers operate in response to temperature changes in hydronic heating systems. They provide spdt switching for three-wire applications. The L6006A,B, and L6007A combine low or high limit and circulator control; L6006C combines circulator control with low and high limit.

The L6006A,B are for horizontal insertion; the A model uses an immersion well; the B model uses a capsule compression fitting for direct immersion. The L6006C is for horizontal or vertical surface mounting. The L6007A is for horizontal or vertical insertion using an immersion well .

Aquastats including a Differential Control

Aquastats in "combination" mode include a feature to support the presence of a tankless coil, by providing a LOW-DIFF control pair; the number of degrees in the DIFF or "differential" setting may vary, but in general the DIFF setting controls the number of degrees of temperature range to be maintained in the boiler to support a tankless coil used to make domestic hot water (washing and bathing).

At AQUASTAT CONTROLS we explain and define the HI LO and DIFF

At AQUASTAT HI LO DIFF SETTINGS we describe the best HI LO DIFF settings to use

At AQUASTAT LO & DIFF DISABLED we explain how to disable the LO and DIFF if you are installing a combination aquastat on a boiler that doesn't sport a tankless coil used for making domestic hot water (for washing and bathing)

Single-purpose Aquastats

Single purpose aquastats are used on older heating equipment and on some water heaters. So if your heating appliance is a water heater that needs only a HI limit and LO limit it may use an aquastat like the Honeywell L6006C1018 offering a boiler temperature range of 65 to 200 deg F while the single purpose HI LO aquastat Honeywell L4006A2007 controls temperatures from 100 to 240 degF and adds a DIFF adjustable between 5 and 30 degF.

You can see that the L4006A2007 would be suitable for a water heater but not a home heating boiler.

Aquastat & Boiler Controls & Information Sources

We provide links just below to several aquastat installation, setting, and adjustment documents in response to reader requests and comments that people sometimes have difficulty finding this information. But readers looking for specific aquastat control information should always first try the control manufacturer.

Reideo (Honeywell) L4006-7-8 High Limit Aquastat cited & discussed at InspectApedia.com

HydroStat boiler control cited & discussed at Inspectapedia.com HydroStat Model 3250 Plus for oil boilers ...

White Rodgers 11A79-2 boiler heater control cited & discussed at InspectApedia.com image adapted from supplyhouse.com 2021 ... White Rodgers 11A79-2 boiler heater control cited & discussed at InspectApedia.com image adapted from supplyhouse.com 2021

White Rodgers 11A79-2 boiler heater control cited & discussed at InspectApedia.com image adapted from supplyhouse.com 2021 ... White Rodgers 11A79-2 boiler heater control cited & discussed at InspectApedia.com image adapted from supplyhouse.com 2021

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-12-15 by Inspectapedia Com Moderator (mod) - review of features & acceptance of the HydroStat Model 3250 Boiler Control

HydroStat boiler control cited & discussed at Inspectapedia.com HydroStat Model 3250 Plus for oil boilers@Cubitus 700,

Thank you for the question; I am researching - the Hydrostat-3250 - and will add information here.

Bottom line:

The Hydrostat 3200-series, including your Hydrostat 3250 boiler control is sold as a "universal" boiler controller that should work just fine with your boiler.

This control from Hydrolevel Co. (a U.S. firm in Connecticut) combines three functions: temperature limit (your old control handled this), Boiler reset - turns off the boiler if unsafe upper limit is reached, your old aquastat also handled this feature), and an economizing feature that, combined with an add-on outdoor temperature sensor, can adjust the boiler's operating temperature range to improve its operating efficiency.

The "Economizer" or as they call it "FuelSmart" feature works like this: at warmer outdoor temperatures the Hydrostat control lowers the operating range of the boiler's limit controls - referred to as "Fuel Smart" technology, though certainly it's not a new idea. You may not use this control on at least some older heating boiler models, including yours, and it can indeed be left "OFF".

When replacing a traditional Aquastat such as your Honeywell Aquastat L8148A, the Hydrostat 3200 control adds a valuable safety feature, a low-water cutoff that I note just below.

This control can also bypass its outdoor temperature sensing FuelSmart feature if the call for heat comes from a "zone" that is actually an indirect-fired water heater, thus assuring that the control can re-heat a domestic hot water supply quickly as well.

Details:

One thing to take from this design is that this control adds a low-water cutoff (LWCO) to the traditional functions of an aquastat like the Honeywell L8148A that you are replacing.

I agree completely with experts who have suggested that adding an LWCO to a residential hydronic heating boiler (they've been used on steam boiler for about a century) adds a valuable safety feature that protects the building, occupants, and the boiler from damage that can happen if a boiler runs low on or out of water.

So on that score it's an improvement over a straight, traditional aquastat replacement.

HydroStat boiler control cited & discussed at Inspectapedia.com HydroStat Model 3250 Plus for oil boilers

An initial review of comments by heating people about the Hydrolevel 3250 found

None of these is a show stopper in my OPINION and merely consulting with the heating supplier when buying a control can avoid the specious error of buying the wrong model.

The Hydrolevel 3250 Aquastat also adds an economizing feature whose use is optional (thus simplifying its installation for some): an outdoor reset feature that, with the addition of an additional sensor (Hydrolevel OS-100 Outdoor Sensor Kit) can provide warm weather shut-down and that can dynamically adjust the boiler's operating temperature range on a call for heat at different outdoor temperatures - a feature that purports to reduce heating costs and improve boiler operating efficiency.

For readers who want to know more about the HydroStat 3250

see HYDROSTAT 3250 BOILER CONTROL - Temperature Limit, LWCO, Boiler Outdoor Temperature & Economizing Features on this same page

(thanks Cubitis for the original link - those are automagically blocked to protect our readers and our website from potential malware or spam)

Adding: a clue to the history of this aquastat is in its patent history including simply the patent dates listed on the HydroStat Model 3250 Plus "Smart Hydrostat" for oil fired heating boilers.

On 2021-12-15 by Cubitus 700 - opinion of the Hydrolevel Aquastat 3250

Question: What would be your opinion of the Hydrolevel Aquastat 3250 for oil burners as a replacement for the Honeywell Aquastat L8148A. It surprising because no one up here appears to know about the hydrolevel. Hydrolevel is a Honeywell company. The 3250 is described as the replacement for the L8148A model in the HYdrolevel literature.

I want to make sure I am being sold the proper equipment. I have an WGO-2 Well McLain which came equipped with the L8148A. It's 20 years old.

The Newer models WGO-2 from Well-McLain come equipped with the Hydrolevel 3250...I thought this would be the best model...but no one has heard about it here, yet it has been manufactured for more than 8 years now.
Thank you
System:

Dual energy
Electric : Thermo2000 20 Kw Electric Boiler

OIl: Well-McLain WGO-2 Oil Boiler 110,000 Btus

1 dual energy Honeywell valve(24 volt)
2 Schneider zone valves (24 volt)
1 Honeywell Primary oil burner control
1 Honeywell L8148A Control (needs to be replaced)
1 Dual energy control (24 Volt)
1 Bell and Gossett circulator (110 volt)

(re posted by Moderator without disallowed link)

Addendum Corrigendum: Hydrolevel is not a Honeywell company, my mistake. As their literature states that Aquastat is a registered trademark of Honeywell (meaning they probably pay royalties to Honeywell to use the descriptive name), I jumped to conclusion that it was a Honeywell company.

But Hydrolevel belongs to the C. Colwes and Co. group which also owns Carlin Combustion Technology, manufacturers of Carlin Burners.

On 2021-11-04 by Inspectapedia Com Moderator (mod)

@jose de la torre,

In the Recommended Articles above you'll find a live link to

AQUASTAT L7224U UNIVERSAL OPERATION & ERROR CODES

On 2021-11-04 by jose de la torre

What is the replacement for the honeywell electronic aquastat model l7148 f 1075 which is discontinued or the best fit?

On 2021-10-11 by inspectapedia.com.moderator (mod)

@Wylie,
Thank you.

We've worked hard on this material for decades, so are really grateful when a reader finds it useful and trustworthy.

We also welcome your photos, questions, criticism or suggestions.

On 2021-10-11 by inspectapedia.com.moderator (mod)

@Wylie,

Yes

On 2021-10-10 by Wylie

@inspectapedia.com.moderator,

Thank you again for your earlier response. I have read the article you suggested and see that it directly relates to the Aquastat model I have installed on my boiler.

Your website and advise are well put together and very helpful. I will be passing the both along.

Thank you again, W.

On 2021-10-10 by Wylie

@inspectapedia.com.moderator,

Thank you for your response. I understand.

The Aquastat is a Honeywell : R8182 Combination Control. Will this Aquastat still fall into the same category of disable the LO limit control in the existing component.

Thanks, W.

On 2021-10-09 by inspectapedia.com.moderator (mod)

@Wylie,

It'd be helpful to know the brand and model of your aquastat.

But on most models there is no need to replace the aquastat when abandoning a tankless coil for domestic hot water. Instead we simply disable the LO limit control in the existing aquastat.

See

https://inspectapedia.com/heat/Aquastat_LO_DIFF_Disable.php AQUASTAT LO & DIFF DISABLED

On 2021-10-09 by Wylie

I have a boiler that was previously used for hot water in the house. Now it is just used for heat. I would like to replace the Aquastat so the use is On-Demand as opposed to keeping the water at a constant heat. I had a guy come over to replace it but he could not for the following reason: "The electronic connection for the Cad Cell is in the Aquastat, not in the burner." He said he doesn't have an On-Demand Aquastat that has the Cad Cell connection in the Aquastat. "It's always in the little box on top of the burner."
Can you please suggest a model that will accommodate my unique needs?
Thanks, W.

On 2020-11-08 by (mod)

Vincent

Please take a look at the two Hackensack cross reference charts Linked In the article above. That's the best way to get exactly the features that you want. It's a bit safer than me making an off-the-cuff guess

On 2020-11-08 by vincent mela

thank you for your response if i did not have a pre heating system and just wanted to control my water temp high and low with no diff what honeywell aquastat would replace the honeywell l8124a-c with thank u

On 2020-11-07 by (mod)

Vincent

I'm embarrassed to have to duck this question. I'm just too worried about your safety to suggest changing out the primary control aquastat on a system I know so little about.

But in general there are certainly single -purpose aquastats that can do what you want.

Watch out: before making any changes I'd give the manufacturer of y ur water pre-heating system a call, to their technical support line, to ask what they recommend.

Stay safe.

DF

On 2020-11-07 13 by vincent mela

i have a outside wood stove that pre heats my boiler water through a heat exchanger my boiler has a honeywell triple aqua stat with a differential i want to replace it with one that has no differential so i can set my boiler to go on when the water temp drops to 120 and run till it hits 160 ?what aqua stat can i replace it with thank you

On 2020-09-19 - by (mod) -

which aquastat to replace a Honeywell L8124A, C

Take a look at the AQUASTAT L7224U articles above at CONTINUE READING or in the ARTICLE INDEX, Greg.

On 2020-09-19 by Greg

I have a honeywell L8124a,c that's all it says, what would I replace it with, the supply houses insist there should be a numbers after it such as l8124a1015?
Thank you

On 2019-11-05 - by (mod) -

Patrick

From the page above we have a couple of Honeywell cross reference charts here's one

inspectapedia.com/heat/Honeywell-Controls-Cross-Reference-Chart.pdf

On 2019-11-04 by Patrick C

I have a Honeywell L4081B 1120 aquastat and need to replace it. What is the replacement or upgraded replacement aquastat I need?

On 2019-08-14 - by (mod) -

You posted this question and we replied at https://inspectapedia.com/heat/Aquastat_Diagnosis_Repair.php

On 2019-08-14 by Joe

My brother has to tap the aquastat on his boiler to turn on the burner to get hot water. His boiler is 45 years old and we got a quote today of $8,000 to replace it.

He is 67 and on Medicaid doesn’t qualify for Social Security. He lives in a small ranch house. $2,200 to repair and not replace.

One time I took the cover off the aquastat and blew in it and it started. Please comment as we are of limited resources.

On 2019-03-19 by TONY

I have an old Honeywell l8048b aquastat on a burnham holiday boiler series 2 and need to replace the aquastat but it is obslete , I need to know which one will work

On 2019-02-13 - by (mod) -

There are a couple of options

Here is an aquastat cross reference chart

https://inspectapedia.com/heat/Honeywell-Controls-Cross-Reference-Chart.pdf

On 2019-02-13 by Brodi

I have a Honeywell 6081A 1036 triple aquastat and need to replace it. What is the replacement or upgraded replacement aquastat I need?

On 2019-02-04 2 - by (mod) -

Forgive me Thomas but

Honeywell HL 6006A1012

is according to Honeywell not a valid product number.

You probably mean the Honeywell L6006 aquastat controller

Yes the L6006A aquastat can control a circulator pump; here's what Honeywell says in their product description

The L6006A,B, and L6007A combine low or high limit and circulator control; L6006C combines circulator control with low and high limit.

The L6006A,B are for horizontal insertion;

the A model uses an immersion well;

the B model uses a capsule compression fitting for direct immersion.

The L6006C is for horizontal or vertical surface mounting. The L6007A is for horizontal or vertical insertion using an immersion well

Please see details about your aquastat at these two links

AQUASTAT L6006A HONEYWELL GUIDE
AQUASTAT L6006A, HONEYWELL [PDF]

in the More Reading links given just above in this article.

On 2019-02-04 by Thomas

Will a Honeywell HL 6006A1012 control a B&G 100BNFI circulator without any other timers or relays?

On 2018-06-24 - by (mod) -

which aquastats can be replaced with the Honeywell, the L7224U

Waume. According to Honeywell, the L7224U

replaces the L8124A, L8124C, L7124U, L7148A, L7248A,C, L7224A,C, and L8148A Controllers.

So yes you could go the other way and use an L8124 A or C,

but

Not necessarily the L8124 B,E,G,L ( https://customer.honeywell.com/resources/techlit/TechLitDocuments/60-0000s/60-0786.pdf )

On 2018-06-24 by wayne o

will or you a L8124B,E,G,L work or replace a L7224U


...

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