Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
AFUE DEFINITION, RATINGS
AGE of CHIMNEYS & FIREPLACES
AGE of AIR CONDITIONERS & HEAT PUMPS
AGE of HEATERS, BOILERS, FURNACES
AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR FILTERS for HVAC SYSTEMS
AIR HANDLER / BLOWER UNITS
AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
ANODES & DIP TUBES on WATER HEATERS
ANTIFREEZE for BOILERS
ANTI SCALD VALVES
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
ASBESTOS IDENTIFICATION IN BUILDINGS
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER VALVE, HEATING SYS
BACKFLOW PREVENTER, HEATER WATER FEEDER
BACKUP HEAT for HEAT PUMPS
BANGING HEATING PIPES RADIATORS
BIO-FUEL PRODUCTION & USE
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BLUE vs YELLOW COMBUSTION FLAMES
BOILER CHEMICAL TREATMENTS
BOILER COMPONENTS & PARTS
BOILER CONTROLS & SWITCHES
BOILER LEAKS CORROSION STAINS
BOILER LEAKS, HOW TO LOCATE
BOILER NOISE SMOKE ODORS
BOILER OPERATING PROBLEMS
BOILER OPERATING STEPS
BOILER PRESSURE & TEMPERATURE SETTINGS
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
BUILDING SAFETY HAZARDS GUIDE
CAPACITORS for HARD STARTING MOTORS
CARBON DIOXIDE - CO2
CARBON MONOXIDE - CO
CHEMICAL TREATMENTS for BOILERS
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEYS & FLUES, ASBESTOS TRANSITE PIPE
CHINESE DRYWALL HAZARDS
CIRCULATOR PUMPS & RELAYS
COOL OFF HEAT, THERMOSTAT SWITCH
COMBUSTION AIR for TIGHT BUILDINGS
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
COMPLETE COMBUSTION, STOICHIOMETRIC
CREOSOTE FIRE HAZARDS
CURVED BRICK CHIMNEYS, SULPHATION
CONDENSING BOILERS/FURNACES DAMAGE
CONVECTOR HEATERS - HYDRONIC COILS
DEFINITION of HEATING & COOLING TERMS
DEFINITIONS of ELECTRICAL TERMS
OIL LINE CONTROLS & VALVES
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DIRECTORY of OIL TANK EXPERTS
DRAFT HOOD, GAS HEATER
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATOR, DAMPER, BOOSTER
DUCT SYSTEM & DUCT DEFECTS
DUST, HVAC CONTAMINATION STUDY
DUST SAMPLING PROCEDURE
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRICAL POWER SWITCH FOR HEAT
EVAPORATIVE COOLING SYSTEMS
FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON THERMOSTAT SWITCH
FAN, COMPRESSOR/CONDENSER UNIT
FAN CONVECTOR HEATERS - HYDRONIC COILS
FAN LIMIT SWITCH
FAN NOISES, HVAC
FILTERS, AIR for HVAC SYSTEMS
FILTERS, OIL on HEATING EQUIPMENT
FIRE SAFETY CONTROLS
FIREPLACES & HEARTHS
FLAME COLOR, BLUE vs YELLOW COMBUSTION
FLOODED HEATING EQUIPMENT REPAIR
FLUE SIZE SPECIFICATIONS
FLUE VENT CONNECTORS
FREEZE-PROOF A BUILDING
FUEL OIL TYPES & CHARACTERISTICS
FUEL UNIT, HEATING OIL PUMPS
FURNACE CONTROLS & SWITCHES
FURNACE HEAT EXCHANGER LEAKS
FURNACE OPERATION DETAILS
FURNACE OPERATING TEMPERATURES
GALVANIC SCALE & METAL CORROSION
GAS BURNER FLAME & NOISE DEFECTS
GAS FIRED WATER HEATERS
GAS PIPING, VALVES, CONTROLS
GAUGES ON HEATING EQUIPMENT
GEOTHERMAL HEATING SYSTEMS
HEAT EXCHANGER LEAK TEST
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT LOSS INDICATORS
HEAT LOSS PREVENTION PRIORITIES
HEAT LOSS R U & K VALUE CALCULATION
HEAT PUMPS, DIAGNOSIS, REPAIR
HEAT TAPES & CABLES for ROOF ICE DAMS
HEATING COST FUEL & BTU COST TABLES
HEATING COST SAVINGS METHODS
HEATING LOSS DIAGNOSIS-BOILERS
HEATING LOSS DIAGNOSIS-FURNACES
HEATING OIL CLOUD WAX GEL POINT
HEATING OIL EXPOSURE HAZARDS, LIMITS
HEATING OIL - OLD, USEABLE?
HEATING OIL PIPING TROUBLES
HEATING OIL SHELF LIFE
HEATING OIL SLUDGE
HEATING OIL TANKS
HEATING OIL TYPES & PROPERTIES
HEATING OIL USAGE RATE
HEATING SMALL LOADS
HEATING SYSTEM INSPECT DIAGNOSE REPAIR
HEATING SYSTEM NOISE DIAGNOSIS
HEATING SYSTEM SERVICE FAQs
HEATING SYSTEM TYPES
HIGH EFFICIENCY BOILERS/FURNACES
HOT WATER HEATERS
HOT WATER IMPROVEMENT
HUMIDITY LEVEL TARGET
ROOF ICE DAM LEAKS
INSULATION INSPECTION & IMPROVEMENT
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
GAS LP & NATURAL GAS SAFETY HAZARDS
MANUALS & PARTS GUIDES - HVAC
METHANE GAS SOURCES
MIXING / ANTI-SCALD VALVES
MIX VALVE SCALD PROTECTION, Best Practices
MOTOR OVERLOAD RESET SWITCH
NATURAL GAS COMBUSTION PRODUCTS
NO HEAT - BOILER
NO HEAT - FURNACE
NOISE / SOUND DIAGNOSIS & CURE
NOISE AIR CONDITIONER / HEAT PUMP
NOISE, DUCT VIBRATION DAMPENERS
NOISE, HEATING SYSTEMS
NOISE, WATER HEATER
ODORS GASES SMELLS, DIAGNOSIS & CURE
ODORS FROM HEATING SYSTEMS
OIL BURNER FUEL UNIT
OIL BURNER INSPECTION & REPAIR
OIL BURNER NOISE SMOKE ODORS
OIL BURNER NOZZLE & ELECTRODES
OIL BURNERS, RETENTION HEAD
OIL BURNER SOOT & PUFFBACKS
OIL FILTERS on HEATING EQUIPMENT
OIL FILTER MISSING
OIL FUEL TYPES & CHARACTERISTICS
OIL HEAT FIRE SAFETY CONTROLS
OIL LINE CLOGGING FIX
OIL LINE QUICK STOP VALVES
OIL LINE SAFETY VALVES, OSVs
OIL FILL PIPE LEAKS
OIL PUMP FUEL UNIT
OIL SPILL CLEANUP / PREVENTION
OIL TANK ABANDONING PROCEDURE
OIL TANKS, BURIED
OIL TANK GAUGES
OIL TANK INSPECTION & TROUBLESHOOTING
OIL TANK LEAKS & SMELLS
OIL TANK PIPING & PIPING DEFECTS
OIL TANK PRESSURE
OIL TANK REGULATIONS
OIL TANK REMOVAL COs
OIL TANK REMOVAL FINANCIAL AID
OIL TANK SAFETY
OIL TANK SLUDGE
OIL TANK STANDARDS - UL
OIL TANK LEAK TEST METHODS
OIL TANK TESTING & REMOVAL COs
OIL TANK WATER REMOVAL
PLASTIC PLEXVENT ULTRAVENT RECALL
PULSE COMBUSTION HEATERS
PRESSURE REDUCING VALVES
PRESSURE REGULATOR, WATER
PUFFBACKS, OIL BURNER
PUMPS, PONY PUMPS
RADIANT HEAT FLOOR MISTAKES
RADIANT HEAT TEMPERATURES
RADIANT SLAB FLOORING CHOICES
RADIANT SLAB TUBING & FLUID CHOICES
RELIEF VALVE LEAKS
RELIEF VALVE, TP VALVE, BOILER
RELIEF VALVE, TP VALVE, STEAM BOILER
RELIEF VALVE, WATER HEATER
RELIEF VALVE, WATER TANK
RESET SWITCH, HEATER PRIMARY CONTROL
RESET SWITCH, HEATER REPAIR
RESET SWITCH, ELECTRIC MOTOR
RESET SWITCH, STACK RELAY
SAFETY HAZARDS & INSPECTIONS
SAFETY HAZARDS GUIDE
SAFETY, HEATING INSPECTION
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SOLAR HEATING SYSTEM DESIGNS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCH, FLUE GAS DETECTOR
SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS
STACK RELAY SWITCHES
STAIN DIAGNOSIS on BUILDING INTERIORS
STEAM HEATING SYSTEMS
THERMAL EXPANSION CRACKS in BRICK
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
THERMAL IMAGING, THERMOGRAPHY
THERMAL MASS in BUILDINGS
THERMAL TRACKING & HEAT LOSS
THERMOSTATS, HEATING / COOLING
THERMOSTATS, WATER HEATER
THERMOSTATIC EXPANSION VALVES
TRANSITE PIPE CHIMNEYS & FLUES
VIDEO GUIDES: HEATING SYSTEMS
VIDEO GUIDES - InspectAPedia.com
WATER HEATER SAFETY
WATER HEATERS for HOME HEATING USE?
WATER HEATER NOISE DIAGNOSIS, CURE
WATER HEATER SCALE DE-LIMING PROCEDURE
WATER HEATER SCALE PREVENTION
WATER SOFTENERS & CONDITIONERS
WINTERIZE A BUILDING
WOOD-OIL COMBINATION HEATERS
WOOD STOVE OPERATION & SAFETY
ZONE VALVES, HEATING
Here we explain the Honeywell L7224U Universal Oil Heating Boiler Electronic Aquastat Controller
This 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 article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
The manual dials that we described 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
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
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... °F/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.
LED Error Codes
The aquastat LED provides will show "err" followed by these eight error codes used by the service technician for diagnostics:
How the L7224U1002 Aquastat Responds to Error ConditionsFor 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
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 on the L7224U1002
Five diagnostic LEDs inside the control provide additional diagnostic features, indicating (counterclockwise from upper left
Trouble Getting the Honeywell L7224U to Work as Specified?
Check the temperature sensor installation on aquastats if behavior is erratic.
[Click to enlarge any image]
Illustrated above is an adapted drawing from the installation instructions for the aquastat discussed in this article, the Honeywell L7224U.
The thermal-grease assures reliable and continuous thermal contact between interior surface of the immersion well on the boiler and the temperature sensing tip of the aquastat's heat probe. Without this grease, thermal movement and possibly even slight corrosion that occur between the surface of the probe and the side of the immersion well can cause the temperature sensor to behave erratically.
The temperature-conductive grease is needed and should be used.
Honeywell feels so strongly on this point that a packet of heat conductive grease is packaged with new aquastats. I've read that the formula for the conductive grease was amended to remove a drying agent, preventing the heat transfer grease from gluing the sensor into the sensor well.
Check that the Aquastat HI, HI-DIFF, LO, LO-DIFF settings are correct and not crossed or in conflict
In the FAQs of this article you'll read that several readers commented about great difficulty getting the Honeywell L7224U aquastat to run the boiler at a sufficiently high temperature and some reported that the HI and LO control functions seem reversed. We suspect that part of the trouble is in pressing buttons to get the right settings past the control's anti-tampering feature.
I include these L7224U adjustment procedure notes from the company's control quick guide linked-to in the citations just below.
Before contacting Honeywell to bug them about how to operate this aquastat, try taking another look at the first 3 PDF files linked-to just below.
If you're still having trouble, Honeywell has also provided a powerpoint training session on this aquastat at http://customer.honeywell.com/NR/rdonlyres/5C67D10A-631C-4404-9149-25BA61F5D8BB/4041/L7224UUNIVERSALAQUASTATTrainingModule.ppt
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.
n 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 (above left) includes a red circle around the aquastat or primary controller on this heater.
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.
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.
Reader Questions: not enough hot water from my L7224U Aquastat-Controlled Boiler
(Feb 18, 2012) MaineMark said:
(Jan 16, 2013) VinceB said:
(Feb 12, 2013) Lonmon said:
Same issue as MaineMark. I have a tankless hot water heater installed for DHW and a long shower will get COLD water at some point. I changed the Hi to 210 and the Lo to 190 in accordance with Burnham the boiler manufacturer recommendations and that helped a bit. They recommended a DIFF of 25 on my old L8124 controller. I left the Hi and Lo DIFF settings at the default of 10. Should i adjust the Lo Diff on this new L7224 controller to maintain better DHW heat?
(Nov 16, 2014) frank hollis said:
Apologies Vince B.
I fixed broken html and added links to Honeywell's instructions for these two controls in the article above. Please take another look.
We are seeing several complaints and notes about confusion in the operation of this control.
Is the LO limit set above the HI or even close to it? The LO needs to be 20 degrees below the HI or it will lock out the upper limit control on many aquastats.
Question: can't set the controls on the Honeywell L7224U
(Nov 17, 2014) FRANK HOLLIS said:
Frank the control has a "lockout to prevent tampering" that can make setting the control tricky.
Try the button pushing procedure shown in Honeywell's
Question: Pennsotti boiler's Riello burner runs just or 10 seconds, same for circulator; short cycling.
(Dec 8, 2014) John said:
John this sounds like a loose wire or a control problem. We don't want short burner on-cycles as it soots-up the system leading to malfunction.
Call the heating service company you use, speak politely with the service manager, ask them to send an experienced technician to your home. I'm afraid that just changing control settings will ignore a soot or operating problem and could leave the system unsafe.
Question:Trouble getting the Honeywell L7224U aquastat to behave - cool boiler, cool baseboards, or crossed controls settings
2 Feb 2015 Anonymous (Gregg) said:
I have a Burnham V14A-T boiler with tankless coil, aquastat is a (Honeywell L7224U1002). I'm not the brightest crayon in the box, but I am the owner/head technician/service engineer for a small CNC machine tool service center. I usually get it right when it comes to figuring out how things are supposed to work, But I must admit, I'm a bit unsure about this.
I recently replaced the old mechanical aquastat on my boiler (about a week ago) it went up in smoke due to poor connections/corrosion in the push loc wire terminals. Any way I replaced it with the Honeywell L7224U1002 unit.
It works I have heat and hot water but not as I understand your explanation of operation, I have second and third guessed myself into a state of frustration, So hopefully you can shed some light on this situation
It seems as though the low limit has complete control over boiler temp. when t-stat is calling for heat. With lo limit at 140 it circulates 130-ish water through the radiators,(140-10 diff) burner running constantly circulator on at 140 off at 130 which is not hot enough to do any good. never gets close to the 210 hi limit.
If I set the lo diff to 25 as suggested to prevent circulator from turning on until 165 I get 115-ish water running through radiators(140-25 diff)It seems the diff is on the - side of lo limit.
The only way I can get hot water for heat is to set lo limit up to 190-10 diff then I get scalded every time I wash my hands, not so bad for me but the wife and grand kids have some unkind things to say about it. If I reduce the lo limit to a safe level the house can't get up to temp. So what am I missing or is this the way its supposed to work?
The old one did pretty much the same thing, we just got used to it. But reading on this site left me with the impression that I did not need to have my boiler at 190 ALL the time, And what you have written makes complete sense to me but that's not what I'm seeing here. 140 domestic 190 heat would be great, Can you help?
Anon - dull crayon
Notes from a not so sharp pencil out of the box: I'm just thinking as typing here. First you can read in the FAQs above that other fellows have had trouble getting this control to behave. I don't know but I suspect that at least part of the problem is that the Honeywell engineers included an anti-tampering feature on the control - to the joy of the HVAC service company - that can make button pushing and control setting sometimes not give you what you thought you set.
Have you taken a look at the quick guide PDF we link in the article above - see
I would not set HI above 200F out of worry for pressing on the TP valve - that is running a bit hot and close to TP valve spill temperatures.
With LO at 140F the HI should be controlling on a call for heat and the LO and DIFF should be sleeping unless the boiler temp is down in the LO / DIFF range
SO I don't assume the control is not working and given that you're a smart Crayola I will for now assume you wired everything correctly and set the control correctly.
SO I ask - could there be another reason the boiler is simply not heating up to the higher temperatures: such as bad flame, or a thick coating of crud on the heat exchanger?
NO because you can foul up the control by crossing its settings - putting the LO up into the too-high range of 190 which then gives you a boiler so hot that the tankless coil is giving scalding water to the sinks. (serves you right)
Yeah it is acting as if the control is crossed somehow.
You could install a tempering valve at your tankless coil so as not to get scalded - that's a good idea in any event.
But I would try this
- turn off power to the control
I include this note from the PDF
Anti-Tampering on the L7224U Aquastat
To discourage unauthorized changing of Aquastat settings, a
procedure to enter the adjustment mode is required. To enter the
HLo= High Limit.
Then press the UP and/or DOWN buttons to move the set point to
the desired value. After 60 seconds without any button inputs, the
The following is for people whose boiler does not include a tankless coil:
To use the L7224U in a cold start boiler application, disable the
Low Limit function by pressing the UP arrow button, DOWN arrow
6 Feb 2015 Gregg said:
Thanks for the reply Dan, I have read all of the suggested material ad nauseum, Both Before and after installing the 7224. Before because I was having trouble with the old mechanical unit. This site actually led me to purchase the 7224.
I can get past the anti tampering lockout, as evident by the fact that I can raise and lower boiler temp by raising or lowering LO LIMIT and/or LO LIMIT DIFF. I have verified that I can circulate 130 degree water, I can circulate 210 degree water, and a few temps in between. That is not the problem here. The problem is when calling for heat, the burner will run constantly until T-Stat is satisfied because the circulator turns on at the LO LIMIT (140)setting.
The circulator will run until Boiler Temp is down to 130 (at -10 diff) then the circulator stops, burner continues to run. round and round it goes, Boiler temp. never gets above LO-LIMIT setting much less to HI LIMIT. If T-Stat is not calling for heat then burner runs until (140)LO-LIMIT is reached and everything stops until boiler cools down to 130, then starts again. Hi LIMIT is ignored completely. The way I understood it to work is the LO-LIMIT is ignored if there is a call for heat. Yes?
5 Feb 2015 Gregg said:
Reply: calling Honeywell for technical assistance with aquastats (maybe)
Let us know what happens, Gregg, and before tearing out any more hair consider you're part of a club of folks who've had trouble setting this control. If still you see no success I'd give Honeywell a call at their tech support line. (The company emphasizes that the control we are discussing should be installed, adjusted, or repaired by a trained HVAC service technician).
Telephone for Honeywell Technical Support with Aquastats or other Heating Controls
5 Feb 2015 Gregg said:
My question is should circulator have stopped when HI-LIMIT -10 was reached then stayed off and restarted only after HI-LIMIT was again reached? Current settings are HL=190, Hdf=10 LL=140 Ldf=25. Duu=OFF ASC=0 PC=OFF
This may be a bit general but on a call for heat the circulator will normally run until either the thermostat is satisfied and the call for heat stops (and turns off the circulator) OR until the boiler temperature drops down into the range controlled by the LO and LO-DIFF (Ldf in your notes).
6 Feb 2015 Gregg said:
I don't know this control as well as I do the old R8182 series. On that control the 10 diff from the HI is hard-wired while the DIFF from the LO is adjustable as described in our article on that control. This L7224U has a programmable DIFF on the HI as well as the LO controls but we ought to re-read the documentation.
Have you considered giving your heating service company or Honeywell a call?
Reader follow-up: trouble finding a heating tech to check the Honeywell L7224U aquastat
[Click to enlarge any image]
Working with Heating Suppliers & Manufacturers: Carol and Oil Burner Soot Visit JEM Supply
Have you asked your local heating service company to help with this problem and have you then asked if they'd call Honeywell to get help with the control? If they learn how to install and troubleshoot the control surely that'll be good for their own business.
Indeed often HVAC suppliers and manufacturers, recognizing that their principal customers are service companies and installers, are reluctant to talk with a homeowner as it infuriates their main customers.
When I first walked into a local HVAC supplier in NY, running my own heating service company with a partner, we had to hand over a business card and convince the supplier that we were "in the business" too (which we were) just to get the time of day. Even then they were nervous, as there were other old-time customers sitting around (looking at the girlie calendars) and who were less than welcoming to a new competitor.
Over time, when the fellows saw we were serious (it helped to walk in through the back door and to arrive covered in soot and smelling of oil burners as well as to know the common names for controls and parts) our relationship blossomed and the supplier was very helpful.
In the 1980's I was working on oil fired heaters in partnership with a woman engineer who was very sharp. Carol S. had built her own car, solar panels, designed computers, and other stuff. And she was very straight and clean-talking (dinked was about the strongest language she'd use). I stepped carefully in demeanor and speech so as to avoid stepping in something. Carol was the boss.
So when she got particularly sooty while squeezing around a dirty oil fired boiler, and when two round black blobs of soot marked her coveralls, I didn't even think of saying a single word about it. Stay focused.
We walked into the service area of JEM supply in Poughkeepsie where about six old timers were sitting around jawing when they should have been out sucking the soot out of oil fired heaters. Silence fell instantly, rolling in not on cats feet but like a silent tsunami of fog. The old guys stared. Behind the counter you could have heard a pin drop.
Nobody said a thing. They all looked at me. They looked at Carol. They looked back at me.
Carol was the boss of our outfit and had more time in the field than I did, but obviously, and as soot blotches demonstrated, she was a woman. Those blots didn't compute easily for the fellows over at JEM supply. They looked at Carol again. They looked away. They looked at me, expecting for me to speak as we walked up to the counter. It was a woman, but obviously we were working on heating systems: Carol was even sootier than I was. We both smelled bad. At least I did.
Carol stepped up to the JEM Supply counter and spoke in her own deep and confident voice.
"Gimme a Sunstrand J-pump 43A, left-hand rotation, with the internal bypass factory set, and a 23-A pump strainer"
Yes maam, said the JEM clerk in a too-loud voice. We took our parts and left. The tsunami of silence surely receded but not before we were driving our truck out of the lot.
See DINK FACTOR - Remember Carol S for another version of this report about our heating company. But don't call us for repairs.
OK so Check These Things on your L7224U Aquastat
Back to bidness: Am I right that you're not seeing any error code on the L7224 aquastat display?
If you're still stuck we could see if Carol will come out of retirement and give us a hand.
Continue reading at AQUASTAT HI LO DIFF SETTINGS that explains the best settings to use & how & when to disable the LOW & DIFF controls or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Please see recent Q&A text moved into the article above
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.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References