Heating Boiler Aquastat Selection
How to select the right boiler aquastat control
AQUASTAT SELECTION GUIDE - CONTENTS: Guide choosing the right heating boiler combination control aquastat or water heater aquastat control, or to replace obsolete aquastats such as the Honeywell L8024B,D with the L8124-series controllers. Honeywell L7224U1002
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
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.
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 th 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
How do I know if the aquastat controller is the right one for my oil burner furnance.
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
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.
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.
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 and 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.
ROBERTSHAW CONTROL CROSS REFERENCE CHART [PDF] or contact Robertshaw Controls, Robertshaw - Headquarters
Itasca, Illinois USA
Customer Service #: +1.800.304.6563 USA,
Controles Temex S. de R.L. de C.V / Robertshaw Laredo Warehouse
Nuevo Laredo, Tamaulipas, Mexico
Customer Service #: +1.956.242.6093,
offices in North America,
Europe, in the Czech Republic, Italy and Slovakia, including Robertshaw - S.R.L.
General Phone #: +39.02.69933.1
Asia, Pacific, including: Robertshaw - (India) Controls Pvt. Ltd.
Survey. No. 197 (Part),Viman Nagar, Nagar Road
Pune, Maharashtra 411 014, India
Office Phone #: +91.020.4912.3300
Australia Pty Limited
North Rocks, NSW 2151 Australia
Customer Service Phone #: +61.296.317.999 Australia, Website: https://www.robertshaw.com/Customer-Service/
Emerson Controls / White Rodgers heater controls are not listed in an easy-to-find cross reference chart; youll have to contact the company or enter a single specific control model number to find the company's recommendation. Since you'll find that trying to contact Emerson Climate Technologies will require you to fill in a web page form and submit it, (pretty dry) we dug out the company's U.S. address: Emerson Climate Technologies Incorporated. 1675 West Campbell Road. Sidney, OH 45365-0669 USA, Phone: 937-498-3011 (The company also has offices in Europe) OR you may prefer to try this White-Rodgers Model Number Search / Cross Reference [WEBSITE]
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 aquaststat 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:
The type of equipment to be controlled: hydronic heating boiler, water heater, solar water heater, something else
The recommendations of the manufacturer of the boiler or water heater in the boiler's or water heater's installation manual
The specific equipment features that need to be controlled: presence or absence of a tankless coil (for domestic hot water supply) or an automatic vent damper, or perhaps working with an outdoor temperature sensor or other energy savings system
The temperature ranges that need to be controlled in the boiler or for its tankless coil - aquastat models also vary in the temperature range that they are intended to control, though most will control boiler temperatures between about 65 degF and 200 degF
The horizontal mounting Honeywell Aquastat No. L8148A1017 provides a DIFF range of 8 deg F while the vertical mounting Honeywell Aquastat No. L8148E1265 provides a DIFF range of 15 degF.
The physical mounting locations for the aquastat controller and the space available for mounting over the boiler's temperature sensing well or at a different spot on the boiler
The mounting position of the aquastat controller: horizontal or vertical. A horizontal mount combination aquastat example is the Honeywell L8148A1017 while a vertical mount combination aquastat example is the Honeywell L8148E1265
Other special features wanted or needed on the aquastat, such as the manual "reset" button on the Honeywell L4006H1004 strap-on aquastat (Note: strap-on aquastats mount directly onto a hot water heating pipe rather than on to the boiler itself - in our opinion this is an obsolete approach that is less reliable than direct-sensor aquastats - see LIMIT CONTROL, SINGLE at inspectapedia.com/heat/Boiler_Heater_Limit_Controls.php )
A vertical mount combination aquastat like the Honeywell L8148E1257 adds a special feature: the control of an automatic vent damper.
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 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 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.
Armstrong 24-hour time and aquastat control accessory: provides on/off pump control according to preset operating times, designed only for use with specified Armstrong Astro series wet roto circulators installed in indoor hot water re circulation applications. Typical timer applications will cycle the pump at preset times, allowing the user to select
operation of the circulating pump during high peak usage periods in order to decrease the
delivery time to outlet fixtures and reduce wasted water, also available at www.honeywell.com
Honeywell Corporation, control installation guides for Honeywell aquastats and other heating and cooling controls: see http://customer.honeywell.com
Honeywell L4008E Aquastat high limit,manual reset, aquastat controller instructions
Honeywell L4006, Manual Reset Strap-On Aquastat (high limit control, 100 to 240 °F) [we consider strap on controls less accurate and reliable than immersion type sensor controls; these were commonly found on older heating boilers including the GE series downfired boilers]
Honeywell L4026B Aquastat control instructions (contact Honeywell Corporation) Here is some basic description of the Honeywell L4026B control, also available at www.honeywell.com
Honeywell L6006 and L6007 Aquastat Controllers, installation instructions for the trained service technician, these controls combine low or high limit and circulator control, with or without an immersion well depending on the control model A,B, C etc., also available at www.honeywell.com
Honeywell L6191 Dual aquastat immersion thermostat, also available at www.honeywell.com
Honeywell L7224 Aquastat Controller, oil electronic controls allowing high limit, high limit differential, low limit, and separate low limit differential settings - set to the specifications of your oil heating equipment manufacturer - 69-1957-1 L7224 Series controls, also available at www.honeywell.com
L7224U1002- is a universal electronic aquastat (replacing over 40 other aquastat models) that provides circulator, burner and boiler temperature control with electronic temperature sensing. The L7224U1002 provides status and diagnostic information through an LED display to enhance the diagnostic process.
In "Run" mode the LED displays the boiler temperature followed by the ambient temperature. Buttons inside the control permit the service tech to scan through the control's settings as well as to change them, much like the functions on a programmable room thermostat. Using the "I" button, the LED display can be cycled through: boiler temperature, high limit, low limit, high differential, low differential, local thermostat status, EnviraCOM thermostat status, Burner status, Circulator status, Zone control, Zone request, Error code, °F/degC.
Five diagnostic LEDs inside the control provide additional diagnostic features, indicating (counterclockwise from upper left) EnviraCOM network active, Thermostat calling for heat, Burner on, Power to zone circulator interrupted (lockout), Circulator powered.
This is a "triple aquastat" providing High, Low, and circulator controls, as well as advanced features permitting electronic configuration and an LED display for diagnostics. This aquastat can provide multiple zone control as well. The L7224U1002 supports Honeywell's EnviraCOM™ communications that permits remote diagnosis as well as OnWatch diagnostics. The low-limit can be disabled for "cold-start" boiler applications such as where no tankless coil is in use.
Eight error codes: 1=sensor fault (check sensor), 2=ECOM fault, check EnviraCOM wiring, 3=Hardware fault, replace the control, 4=B1 fault, check B1 wiring/voltage, 5=Low line voltage, check L1/L2 110VAC, 6=Fuse, check ECOM wires, replace fuse, 7=EEPROM limit and differential settings, restore to desired settings, 8=Repeated B1 fault, (voltage present at B1 when output is turned off); check B1 wiring/voltage
Honeywell link for a powerpoint training session on this aquastat: http://customer.honeywell.com/NR/rdonlyres/5C67D10A-631C-4404-9149-25BA61F5D8BB/4041/L7224UUNIVERSALAQUASTATTrainingModule.ppt
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Ask a Question or Search InspectApedia
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones