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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
BIOGAS 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 NOISES
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
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OIL LINE SAFETY VALVES, OSVs
OIL FILL PIPE LEAKS
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PLASTIC PLEXVENT ULTRAVENT RECALL
PULSE COMBUSTION HEATERS
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SAFETY HAZARDS & INSPECTIONS
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SOLAR HEATING SYSTEM DESIGNS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCH, FLUE GAS DETECTOR
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STACK RELAY SWITCHES
STAIN DIAGNOSIS on BUILDING INTERIORS
STEAM HEATING SYSTEMS
THERMAL EXPANSION CRACKS in BRICK
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THERMAL EXPANSION of MATERIALS
THERMAL IMAGING, THERMOGRAPHY
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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 NOISES
WATER HEATER SCALE DE-LIMING PROCEDURE
WATER HEATER SCALE PREVENTION
WATER SOFTENERS & CONDITIONERS
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE 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.
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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
Five diagnostic LEDs inside the control provide additional diagnostic features, indicating (counterclockwise from upper left
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
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.
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.
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