Guide to the Honeywell L7224U Universal Oil Heating Boiler Electronic Aquastat Controller, Settings & Error Codes
InspectAPedia^® -

Guide to the Honeywell L7224U1002 Universal Oil Heating Boiler Electronic Aquastat Controller
Installation & service guide for the L7224U1002
L7224U1002 Technicians Quick Reference Guide #69-1957 - Error Codes
How to set the HI LO and DIFF on a heating boiler control
Links to common heating control aquastat installation and adjustment instructions
Questions & Answers about Aquastats and Hot Water Heating Equipment Controls - the Honeywell L7224U

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.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.

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.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

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

See L7224U1002 Technicians Quick Reference Guide #69-1957
The Honeywell L7224U Oil Electronic Aquastat Controller - 69-1720-2 series instructions are provided in a PDF, a power point classroom presentation, and in a L7224U1002 Technicians Quick Reference Guide #69-1957 (originals from Honeywell, copies here).

Questions & Answers about Aquastats and Hot Water Heating Equipment Controls

Where is the aquastat located on heating equipment?

Aquastat location on a heating boiler (C) D Friedman

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.

Strap on aquastat (C) Carson Dunlop Assoc

Some older heating systems used a "strap-on" aquastat that is clamped to a hot water pipe just above the heating appliance - shown at left, courtesy of Carson Dunlop Associates.

See Strap-On Limit Controls

Questions & Answers regarding this article

Questions & Answers about Aquastats and Hot Water Heating Equipment Controls - the Honeywell L7224U and similar controls

Ask a Question or Search InspectAPedia

HTML Comment Box is loading comments...

Recommend / Share this Article

...

Technical Reviewers & References

InspectAPedia.com^® - Daniel Friedman - Publisher & Editor.
InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

BOILERS, HEATING
  BOILER OPERATION DETAILS
  BOILER CONTROLS & SWITCHES
  Air Bleeder Valves
  Air-bound boilers & radiators
  Air Scoops Purgers Separators
  AQUASTAT CONTROL Functions
    Aquastat control HI LO settings
    Aquastat control DIFF settings
    Disabling LO & DIFF     L7224U Universal Aquastat
    Single Function Limit Switches
    Strap-On Limit Controls
  CAD CELL RELAY SWITCH
  CHECK VALVES, HEATING SYSTEM
  Chemical treatments, Boiler
  Circulator Pumps & Relays
  ELECTRIC MOTOR OVERLOAD RESET SWITCH
  ELECTRICAL POWER SWITCH FOR HEAT
  Expansion Tanks
  FIRE SAFETY CONTROLS
  Gauges on Heating Equipment
  Limit Switches, Boilers
  Low Water Cutoff Valves, Boilers
  MIXING / ANTI-SCALD VALVES
  RELIEF VALVES - TP VALVES
  Reset Switch - Primary Control
  Reset Switch - electric motors
  SPILL SWITCHES
  STACK RELAYS
  THERMOSTATS, HEATING / COOLING
  Water Feeder Valves, Hydronic Boiler
  Zone Valves

Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspect ion services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
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

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book 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. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

Hot Air Heating Furnace Basic Operating Steps
Guide to Heating System Components:
Air Bleeder Valves for Hot Water Heating Systems: Radiators, Baseboards, Convectors
Aquastats Heating Boiler Primary Controls: A guide to Aquastats for control of hot water heating boilers and tankless coils
BLUE vs YELLOW COMBUSTION FLAMES - the Blueray history and blue flame vs. yellow flame combustion, flame color & combustion efficiency, & how oil competes with gas as a heating fuel.
CAD CELL RELAY SWITCH on oil fired furnaces or boilers as flame sensors & safety devices
Check Valves Guide to check valves and back flow preventers on hydronic (hot water) heating systems (gas or oil fired)
Draft Hoods on gas fired heating equipment, function and safety
Draft Regulators & barometric dampers on oil fired heating equipment
Expansion Tanks Guide to pressure control and expansion tanks on hydronic (hot water) heating systems (gas or oil fired)
Fan Limit Switch on hot air furnace heating systems (gas or oil fired)
Flue Gas Spill Switch on gas fired heating equipment sense combustion and protect from blocked flues
Gas Piping, Valves, Controls including gas regulator assembly and other controls
Heat Won't Turn Off - Stop Unwanted Heat explanation of why heat may continue to come out of radiators or baseboards even though you have turned down the thermostat
MIXING / ANTI-SCALD VALVES: Guide to mixing valves on hot water heating systems and radiant heat systems
Power Switches to turn on or off heaters for furnaces & boilers, oil & gas fired, heat pumps or electric furnaces or boilers
RELIEF VALVES - TP VALVES: A guide to temperature and pressure relief valves & safety controls on hot water and steam heating systems
Stack Relay Switches Explained on oil fired furnaces or boilers as flame sensors & safety devices
Thermostats & Heat Controls for furnaces & boilers, oil & gas fired, heat pumps or electric furnaces or boilers
Water Feed Valves: A guide to water-feeding/pressure-reducing valves on hot water and steam heating systems
Zone Valves: A guide to zone valves for heating zone control on hot water heating systems
Carbon Dioxide Gas Toxicity
Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
DUST CONTAMINATION FROM HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
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.)
...

Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair

Ask a Question or Search InspectAPedia

Guide to the Honeywell L7224U Universal Oil Heating Boiler Electronic Aquastat Controller

Basic Boiler Operation & Control Sequence using an Aquastat

What's New in the Honeywell L7224U1002 Universal Replacement Aquastat

Explaining the LED display on the Honeywell L7224U1002

LED Status Displays

LED Error Codes

How the L7224U1002 Aquastat Responds to Error Conditions

Individual Diagnostic/Status Green LEDs

Questions & Answers about Aquastats and Hot Water Heating Equipment Controls

Where is the aquastat located on heating equipment?

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair