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 Guide to the Honeywell L7224U Universal Oil Heating Boiler Electronic Aquastat Controller, Settings & Error Codes
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Here we explain the Honeywell L7224U Universal Oil Heating Boiler Electronic Aquastat Controller - an updated Honeywell® combination control that sets boiler temperature and may also control hot water production via a tankless coil on the heating boiler. The photo above shows the interior of a Honeywell L7224U combination heating control, also called an "aquastat". This aquastat model includes the "universal" term in its name because it can replace more than 40 older heating boiler controls. This website answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.
Readers who are not familiar with this control should review the definitions and functions of aquastats and the aquastat HI, LO, and DIFF settings found on older boiler controls, starting at AQUASTAT CONTROL Functions. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Guide to the Honeywell L7224U Universal Oil Heating Boiler Electronic Aquastat Controller
The manual dials that we described above at AQUASTAT CONTROL Functions and at Aquastat control HI LO settings and for Hi, Lo, and at Aquastat control DIFF settings for DIFF disappear on the newer L7224U1002 Universal Oil Heating Boiler Electronic Aquastat Controller from Honeywell.
However the concepts and the actual settings of High limit, Low Limit, and differentials remain about the same for this and most other aquastat controls used on hydronic boilers, except that this new control adds additional levels of control including the ability to replace the "fixed" high limit DIFF on older aquastats with a set-variable High Limit DIFF on the new control.
This new control also adds both a two-character error code display and a collection of LEDs to assist the service technician in problem diagnosis and control setting.
And the basic operation of this control in operating the oil burner and/or zone circulators is about the same as well.
Basic Boiler Operation & Control Sequence using an Aquastat
On a call for heat from the thermostat, the zone circulator starts when water temperature is
above Low Limit setting (if applicable - that is, if this feature is enabled - the default). The heating boiler
temperature is checked. The burner starts when the
water temperature is below High Limit setting.
When the boiler temperature reaches or exceeds the High Limit, the burner is turned off. The burner restarts when the
water temperature drops back below the High Limit
setting minus the differential. As long as the circulator is continuing to call for heat and provided the control has not "locked out" the circulator (as we discussed above) the zone circulator will continue to circulate hot water through the heating zone.
When the thermostat is satisfied - that is room temperature has reached the thermostat setting, the circulator and burner are turned off.
What's New in the Honeywell L7224U1002 Universal Replacement Aquastat
These newer aquastat controllers are often used to replace the older Honeywell L8124A series that was and remains widely used, also available at www.honeywell.com.
The Honeywell L7224U1002 Universal Oil Heating Boiler Electronic Aquastat Controller is a universal electronic aquastat (replacing over 40 other aquastat models) that provides circulator, burner and boiler temperature control with electronic temperature sensing.
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 on this control can be disabled for "cold-start" boiler applications such as where no tankless coil is in use.
Explaining the LED display on the Honeywell L7224U1002
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 ("bt"...temperature... degF/degC). Three control 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.
Watch out: homeowners should not mess with the control settings. Doing so can lead to loss of heat, and/or costly and embarrassing service calls.
LED Status Displays
Using the "I" button, the LED display can be cycled through the individual status displays listed below. Cycling to each topic, the display shows in succession two or three readings: the identity of the item being displayed, the reading, and a F or C display for Fahrenheit of Centigrade (where applicable). The service technician uses a quick reference guide to decode these readings.
- Boiler temperature - current temperature sensed by the sensor bulb
- High limit setting - (130 to 240 degF)
- Low limit setting - (110 - 220 degF)
- High limit differential setting - (5-20 degF) (this is a new feature; above we said that this figure was fixed in the control)
- Low limit differential setting - (10-25 degF)
- Local thermostat status (calling for heat or not)
- EnviraCOM thermostat status
- Burner status
- Circulator status
- Zone control
- Zone request
- Error code (see below for the error codes)
- degF/degC - how temperature should be displayed
LED Error Codes
The aquastat LED provides will show "err" followed by these eight error codes used by the service technician for diagnostics:
- 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
How the L7224U1002 Aquastat Responds to Error Conditions
For error conditions 1-5 listed above,
when an error condition is detected, all outputs
except ZC are shut down. Burner is off. The control
continues to function and restarts when error is
corrected. During the error check sequence, the
system checks for drift in the sensor and
corrosion in the connections.
If error conditions 6 or 7 is detected, the control has
reset the High Limit, Low Limit and Differential setting to a default value and will continue to
run at those settings. Performance of the system
will be degraded, but every effort is being made to keep heat safely on in the building pending further diagnosis and repair.
If error condition 8 is detected, all outputs
except ZC (the circulator control) are shut down. The burner is off.The control
continues to function and restarts when all three
user keys have been pressed longer than 60
seconds.
Watch out: homeowners should not mess with the control settings. Doing so can lead to loss of heat, or in this case possibly an unsafe condition, and/or costly and embarrassing service calls.
COMMENT: it was instructive to review the Honeywell service literature on the control as it directs the oil heat service technician to check wiring and voltages, but leaves to the technician the observation of an oil burner shut down due to dirty or sooty operation, fuel problems, or similar issues. The control monitors electrical conditions and temperature. Separate safety controls such as the flame-sensing cad cell (CAD CELL RELAY SWITCH) perform additional functions such as flame detection and dirty or sooty operation.
Individual Diagnostic/Status Green LEDs
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.
Honeywell has provided a powerpoint training session on this aquastat at http://customer.honeywell.com/NR/rdonlyres/5C67D10A-631C-4404-9149-25BA61F5D8BB/4041/L7224UUNIVERSALAQUASTATTrainingModule.ppt
Questions & Answers about Aquastats and Hot Water Heating Equipment Controls
Where is the aquastat located on heating equipment?
Because the aquastat is a control used on hot water heating systems it will be located most often right on the heating boiler or water heater.
That's because the aquastat includes a temperature sensor that has to be inserted into the water being heated so that the water temperature is monitored.
On some installations the aquastat may be wall-mounted next to the heating unit and connected to it by a flexible probe line whose end is inserted into a temperature sensing well right on the heater unit.
Our photo of a modern hydronic (hot water) heating boiler (left) includes a red circle around the aquastat or primary controller on this heater. |
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Frequently Asked Questions (FAQs) about the Honeywell Aquastat such as the L7224U
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. 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:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
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 Home Reference Book, a reference & inspection report product for building owners & inspectors.
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.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- 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.
- 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.
- Thanks to Bottini Fuel service manager Ron Thomas for discussing aquastat functions, low limit controls, oil burner short cycling causes, and boiler maintenance, reliability, and service contracts 4/13/2010. Bottini Fuel is a residential and commercial heating oil distributor and oil heat service company in Wappingers Falls, NY and with offices in other New York locations. Bottini Fuel, 2785 W Main St,
Wappingers Falls NY, 12590-1576
(845) 297-5580 more contact information for Bottini Fuel
- 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 L4041A,C Pool Heater Aquastat Controller Instructions, also available at www.honeywell.com
- Honeywell L4006, Manual Reset Strap-On Aquastat (high limit control, 100 to 240 degF) [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 L4029 Reset Limit Control, also available at www.honeywell.com
- Honeywell L4103A,B,C Combination Aquastat and High Limit Controller Instructions, also available at www.honeywell.com
- Honeywell L6006A Aquastat Controller installation instructions, 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
- Honeywell L7224U Oil Electronic Aquastat Controller - 69-1720-2 series instructions. These newer aquastat controllers are often used to replace the older Honeywell L8124A series that was and remains widely used, 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, degF/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
- See L7224U1002 Technicians Quick Reference Guide #69-1957
- Honeywell L8124A,B,C,E,G,LO,M Aquastat Relays immersion type controllers for forced hydronic heating systems that include domestic hot water service (such as a tankless coil), also available at www.honeywell.com
- Honeywell R8182D,H Combination Protectorelay™ Primary Control and Aquastat® Controller Installation Instructions combination protectorelay Primary Control installation and operations manual, also available at www.honeywell.com
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 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.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
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.
- Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
- 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.
- The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
- Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
- The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
- Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
- "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- "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
- "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
- 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
- Installation Guide for Residential Hydronic Heating Systems
- Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
- The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
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