Boiler Fault Codes
Fire-tube, water-tube, condensing, and combi boiler diagnostics plus burner-management codes for Lochinvar, Weil-McLain, Cleaver-Brooks, Fulton, AERCO, Viessmann, Honeywell, Fireye, Siemens, and more.
Coverage
667codes
18 controllers across 18 brands
Filter by brand / controller
Browsing all 667 codes · page 1 of 14
Lochinvar · SMART SYSTEM / SMART TOUCH
Ignition Failure — Ignition Failure / No Flame Established
Boiler attempted to ignite but did not detect a flame within the trial-for-ignition period.
Likely Causes
- Gas supply off or low pressure
- Faulty igniter or igniter cable
- Dirty or failed flame sensor
- Gas valve not opening
First Checks
- Verify gas supply valve is open
- Check gas supply pressure (4-14" w.c. NG, 8-14" LP)
- Inspect igniter for damage or debris
- Test flame sensor rod continuity
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C; lochinvar_boiler_trouble_codes.pdf (wsimg.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Flame Loss — Flame Loss During Run
Flame was established but was lost during normal operation.
Likely Causes
- Gas pressure fluctuation
- Dirty or failing flame sensor
- Draft problem causing flame out
- Gas valve failing
First Checks
- Check gas pressure stability during operation
- Clean or replace flame sensor rod
- Inspect venting for blockage or backdraft
- Check gas valve operation
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C
Lochinvar · SMART SYSTEM / SMART TOUCH
High Limit — High Water Temperature Limit
Boiler outlet water temperature exceeded the high-limit setting (typically 210°F). Manual reset required.
Likely Causes
- Low or no water flow through boiler
- Closed or failed zone valve
- Failed pump
- Scaled heat exchanger
First Checks
- Verify boiler pump operation on call for heat
- Check system for closed valves
- Confirm system is full of water and air-purged
- Measure delta-T across boiler
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C
Lochinvar · SMART SYSTEM / SMART TOUCH
Gas Pressure SW — Gas Pressure Switch Fault
Optional manual-reset low or high gas pressure switch has tripped. Manual reset required after correcting condition.
Likely Causes
- Gas supply pressure too low (<4" w.c. NG)
- Gas supply pressure too high (>14" w.c. NG)
- Missing jumper if switches not installed
- Loose wiring at Low Voltage Connection Board
First Checks
- Reset pressure switches after correcting pressure
- Measure supply gas pressure
- Check for loose/missing jumper on Low Voltage Connection Board
- Verify no additional device wired across gas pressure switch terminals
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C; lochinvar_boiler_trouble_codes.pdf
Lochinvar · SMART SYSTEM / SMART TOUCH
Flow Switch/LWCO — Flow Switch / Low Water Cutoff Fault
Optional flow switch or low water cutoff device is open. Manual reset required after correcting condition.
Likely Causes
- Pump not running
- Closed valve or obstruction in piping
- System low on water
- Air in system
- Blown fuse F3 on control board
First Checks
- Check boiler pump operation on call for heat
- Check for closed valves or obstructions
- Verify system is full of water and air has been purged
- Replace fuse F3 on control board if blown
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C; lochinvar_boiler_trouble_codes.pdf
Lochinvar · SMART SYSTEM / SMART TOUCH
Blocked Drain SW — Blocked Drain Switch / Condensate Backup
Blocked drain switch detected excessive condensate buildup inside the unit. Manual reset required.
Likely Causes
- Condensate drain tube kinked or blocked
- Condensate trap plugged
- Loose wiring at drain switch harness
- Failed blocked drain switch
First Checks
- Inspect condensate tube for obstructions
- Inspect and clean condensate trap
- Check wiring harness plug at drain switch
- Replace blocked drain switch if faulty
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C; lochinvar_boiler_trouble_codes.pdf
Lochinvar · SMART SYSTEM / SMART TOUCH
Flue Temp High — High Flue Temperature Lockout
Flue gas temperature exceeded maximum allowable limit. Indicates abnormal combustion or blocked heat exchanger.
Likely Causes
- Fouled or scaled heat exchanger
- Incorrect gas valve calibration
- Blocked flue sensor
- Combustion tuning issue
First Checks
- Verify flue sensor location in flue outlet
- Check heat exchanger for scale or debris
- Review combustion analysis
- Check flue sensor wiring
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C; Crest Modbus Register List (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Air Pressure SW — Air / Flue Pressure Switch Fault
Combustion air proving switch or blocked flue switch did not make within the expected time frame.
Likely Causes
- Blocked air intake or flue
- Failed or sticky pressure switch
- Loose tubing to pressure switch
- Failed combustion blower
First Checks
- Inspect air intake and flue for blockage (ice, debris)
- Verify combustion blower starts and runs to speed
- Check pressure switch tubing for cracks
- Test pressure switch with manometer
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C; combiboiler.ca/lochinvar
Lochinvar · SMART SYSTEM / SMART TOUCH
Blower Fault — Combustion Blower Fault
Combustion blower (fan) did not reach commanded speed within the expected time, or lost speed during operation.
Likely Causes
- Failed blower motor
- Blower obstructed
- Blower control board fault
- Wiring failure to blower
First Checks
- Listen for blower startup; verify it reaches speed
- Inspect blower wheel for debris or damage
- Check 120VAC supply to blower
- Check wiring harness from control board to blower
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C; combiboiler.ca/lochinvar
Lochinvar · SMART SYSTEM / SMART TOUCH
Gas Valve Fault — Gas Valve Circuit / Modulation Fault
Gas valve circuit fault — modulating valve cannot reach commanded position, or a wiring fault exists.
Likely Causes
- Failed gas valve
- Broken or shorted gas valve wiring
- Main control board output failure
- Gas valve coil failure
First Checks
- Check 24VAC at gas valve terminals on call for heat
- Inspect gas valve wiring harness for damage
- Verify gas valve resistance per service manual
- Replace gas valve if coil open or shorted
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C; combiboiler.ca/lochinvar
Lochinvar · SMART SYSTEM / SMART TOUCH
Supply Sensor Fault — Outlet (Supply) Temperature Sensor Fault
Outlet water temperature sensor is reading out of range (open or short circuit).
Likely Causes
- Sensor connector loose or disconnected
- Damaged sensor cable
- Failed NTC temperature sensor
- Water ingress in sensor pocket
First Checks
- Check wiring connector at sensor
- Measure sensor resistance and compare to chart in service manual
- Inspect sensor for physical damage
- Replace sensor if resistance out of range
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C
Lochinvar · SMART SYSTEM / SMART TOUCH
Return Sensor Fault — Return Water Temperature Sensor Fault
Return (inlet) water temperature sensor is reading out of range.
Likely Causes
- Sensor connector loose
- Damaged sensor cable
- Failed NTC sensor
- Sensor installed incorrectly
First Checks
- Check wiring at sensor connector
- Measure sensor resistance vs. chart (Table 3-2)
- Inspect sensor for physical damage
- Replace sensor
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C
Lochinvar · SMART SYSTEM / SMART TOUCH
Flue Sensor Fault — Flue Temperature Sensor Fault
Flue temperature sensor is open or reading out of range.
Likely Causes
- Sensor not installed in flue outlet
- Sensor wiring disconnected
- Failed sensor
- Sensor cable damage from high flue temp
First Checks
- Verify sensor is physically located in the flue outlet
- Check wiring connections at sensor
- Measure sensor resistance and compare to spec
- Replace sensor if faulty
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C
Lochinvar · SMART SYSTEM / SMART TOUCH
Outdoor Sensor Fault — Outdoor Temperature Sensor Fault
Outdoor reset sensor is open or out of range. Boiler will operate without outdoor reset until corrected.
Likely Causes
- Sensor lead broken by weather or UV exposure
- Connector disconnected at control board
- Failed sensor
- Sensor location shielded from outdoor air
First Checks
- Inspect outdoor sensor cable for damage
- Check connector at main control board
- Measure sensor resistance at various outdoor temps
- Replace sensor if faulty
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C
Lochinvar · SMART SYSTEM / SMART TOUCH
Cascade Comm Fault — Cascade / BMS Communication Fault
Communication lost between cascaded boilers or between the boiler and a Building Management System (BMS).
Likely Causes
- BMS communication cable disconnected or broken
- Incorrect Modbus/BACnet configuration
- Incorrect slave ID or baud rate
- Termination resistor missing
First Checks
- Check physical Modbus/BACnet cable connections
- Verify dip switch configuration on MTR-01 board
- Confirm baud rate and slave ID match BMS settings
- Check for 120-ohm terminating resistors at ends of network
Source: Lochinvar Crest Modbus Register List (ccontrols.com); lochinvar_error_codes.pdf
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-01 — Blocking: Space Heating Demand Blocked
Space heating demand blocked by the control (WWSD active or BMS command).
Likely Causes
- Warm weather shutdown (WWSD) active
- Outdoor air temp above WWSD setpoint
- BMS command to block SH
- Cascade leader is blocking
First Checks
- Check WWSD setpoint vs. current outdoor temperature
- Review BMS command to boiler
- Check outdoor air sensor reading
- Verify cascade leader status
Source: Lochinvar Crest Modbus Register List, blocking code 1 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-02 — Blocking: Low 24VAC Supply
24VAC control voltage is below minimum threshold; boiler blocked from starting.
Likely Causes
- Transformer undersized or failing
- Excessive external load on 24V circuit
- Wiring fault creating voltage drop
- Transformer primary voltage low
First Checks
- Measure 24VAC at control board
- Check for additional devices on 24V circuit
- Inspect transformer output
- Verify supply voltage to boiler
Source: Lochinvar Crest Modbus Register List, blocking code 2 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-04 — Blocking: MRHL Open (Manual Reset High Limit)
Manual reset high limit switch is open. Boiler will not fire until switch is manually reset.
Likely Causes
- High temperature event previously occurred
- Wiring to limit switch open
- Failed manual reset limit switch
- Jumper missing if limit not installed
First Checks
- Identify and correct cause of previous high-temp event
- Press reset button on manual reset high limit
- Check wiring continuity to limit switch
- Replace limit switch if faulty
Source: Lochinvar Crest Modbus Register List, blocking code 4 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-07 — Blocking: High Delta-T (Outlet-Inlet)
Temperature differential between boiler outlet and inlet exceeds maximum allowed value. Firing rate is being limited.
Likely Causes
- Low system flow rate
- Air locked in system
- Closed zone valves
- Undersized pump
First Checks
- Verify pump is running and at correct speed
- Check all zone valves are open
- Purge air from system
- Measure actual supply/return temperatures
Source: Lochinvar Crest Modbus Register List, blocking code 7 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-08 — Blocking: High Flue Temperature
Flue temperature is elevated; controller is limiting maximum firing rate.
Likely Causes
- Scale or fouling on heat exchanger
- Combustion tuning too rich
- Flue sensor malfunction
- Restricted flue
First Checks
- Check heat exchanger for scale buildup
- Review combustion analysis
- Inspect flue for partial blockage
- Verify flue sensor reading accuracy
Source: Lochinvar Crest Modbus Register List, blocking code 8 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-14 — Blocking: DHW Tank Demand Blocked (Fan Problems)
DHW tank demand blocked because combustion fan has reported a problem.
Likely Causes
- Fan motor fault
- Fan speed sensor failure
- Fan obstructed
- Fan control signal wiring fault
First Checks
- Listen and confirm fan spins up on demand
- Check fan speed feedback wire
- Inspect fan inlet for obstruction
- Measure voltage supply to fan motor
Source: Lochinvar Crest Modbus Register List, blocking code 14 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-16 — Blocking: Outlet Temperature Limit
Boiler outlet water temperature has reached the set limit; firing rate is reduced or blocked.
Likely Causes
- Setpoint too close to limit
- Low flow causing rapid temp rise
- Demand setpoint higher than design
- Sensor reading high
First Checks
- Compare current outlet temp to limit setting
- Check flow rate through boiler
- Review temperature setpoint programming
- Verify sensor accuracy
Source: Lochinvar Crest Modbus Register List, blocking code 16 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-24 — Blocking: High Temperature Rise
Temperature rise from inlet to outlet is exceeding allowable rate. Firing rate is being capped.
Likely Causes
- Low flow rate causing high delta-T
- Bypass valve stuck closed
- Air-locked system
- Pump failure
First Checks
- Verify pump is operational
- Check for air in system
- Inspect bypass valve if installed
- Measure actual inlet and outlet temperatures
Source: Lochinvar Crest Modbus Register List, blocking code 24 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-26 — Blocking: High Outlet Water Temperature
Outlet water temperature exceeds software high-limit setpoint, preventing firing.
Likely Causes
- Setpoint too low relative to actual load
- Sensor offset error
- High-limit set too close to operating setpoint
- Demand calling unexpectedly
First Checks
- Review high-limit setpoint in SMART SYSTEM parameters
- Check temperature sensor accuracy
- Verify demand type and source
- Allow boiler to cool before restart
Source: Lochinvar Crest Modbus Register List, blocking code 26 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Block-27 — Blocking: Anti-Cycling Time Active
Boiler is in anti-cycling delay period and will not restart until the delay has elapsed.
Likely Causes
- Normal operation after recent shutdown
- Oversized boiler for load
- Short-cycling load profile
First Checks
- Wait for anti-cycling delay to expire
- Review boiler sizing for the load
- Check minimum off-time setting in parameters
Source: Lochinvar Crest Modbus Register List, blocking code 27 (ccontrols.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Low Water — Low Water Pressure / Low Water Cutoff
System water pressure is below minimum threshold or the low-water cutoff device has opened.
Likely Causes
- System pressure below 10 PSI
- Leak in system
- Expansion tank waterlogged or failed
- Fill valve not maintaining pressure
First Checks
- Check system pressure gauge (should be 12-15 PSI cold)
- Inspect system for water leaks
- Check expansion tank pre-charge
- Verify automatic fill valve operation
Source: Lochinvar FTXL User Manual 100361312; combiboiler.ca/lochinvar
Lochinvar · SMART SYSTEM / SMART TOUCH
O-Temp HEX — Over-Temperature Heat Exchanger Switch
Thermal fuse or over-temperature switch on the heat exchanger body has opened, indicating extreme localized temperature.
Likely Causes
- No water flow through heat exchanger
- Scale buildup causing hot spots
- Failed thermal fuse
- Fire from previous ignition fault
First Checks
- Restore water flow before attempting reset
- Check heat exchanger for scale
- Test thermal switch/fuse continuity
- Replace thermal fuse if blown
Source: Lochinvar Knight XL Service Manual KBXII-SER Rev C (O-temp HEX switch added Rev C)
Lochinvar · SMART SYSTEM / SMART TOUCH
Stack Temp Limit — Stack Temperature High Limit (Power-Fin)
Stack (flue gas) temperature has exceeded the high-limit setting on the Power-Fin boiler.
Likely Causes
- Scale or fouling in heat exchanger
- Incorrect combustion air/fuel ratio
- Flue gas bypass damper open
- Failed stack sensor
First Checks
- Read actual stack temperature from display
- Inspect heat exchanger for deposits
- Perform combustion analysis
- Verify stack temperature sensor operation
Source: Lochinvar Power-Fin Service Manual 596898100280636_2000538993 Rev H (lochinvar.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Inlet Temp High — High Inlet Water Temperature
Inlet water temperature to the boiler exceeds maximum allowed value, preventing firing to avoid thermal shock.
Likely Causes
- Return water from system too hot (>180°F)
- System mixing valve failed
- Pipe crossover between supply and return
- Heat stored in large volume system
First Checks
- Measure actual inlet temperature
- Check for hydraulic short circuit
- Verify mixing valve is operating correctly
- Review piping diagram for cross-connections
Source: Lochinvar Power-Fin Service Manual 596898100280636_2000538993 Rev H
Lochinvar · SMART SYSTEM / SMART TOUCH
System Sensor Fault — System Header Sensor Fault
Header or system sensor (cascade/modular systems) is open or out of range.
Likely Causes
- Sensor disconnected from header well
- Sensor wiring damage
- Failed sensor
- Incorrect sensor type installed
First Checks
- Check sensor physically seated in well
- Inspect wiring back to control board
- Measure resistance and compare to spec
- Replace sensor if out of tolerance
Source: Lochinvar Crest Modbus Register List (ccontrols.com); blocking code 15
Lochinvar · SMART SYSTEM / SMART TOUCH
Waterside Pressure — Waterside Pressure Fault (FTXL)
FTXL fire tube boiler detected low system water pressure below minimum operating pressure.
Likely Causes
- System pressure below 10 PSI
- Leak in system
- Fill valve failure
- Expansion tank failure
First Checks
- Check pressure at boiler gauge
- Inspect system for leaks
- Check expansion tank
- Verify automatic fill valve operation
Source: Lochinvar FTXL User Manual 100361312_2000617081 Rev A (lochinvar.com)
Lochinvar · SMART SYSTEM / SMART TOUCH
Service Due — Service Due Notification
Annual service reminder has triggered. Boiler continues to operate but service is needed.
Likely Causes
- Service interval timer elapsed (typically 12 months)
- First startup notification not cleared
First Checks
- Perform annual service and reset service notification from SMART SYSTEM menu
- Follow procedure shown in YouTube video eblTFsymZb0 for reset
Source: Lochinvar Knight SMART SYSTEM service notification (YouTube: eblTFsymZb0)
Lochinvar · SMART SYSTEM / SMART TOUCH
E119 — Low Gas Pressure During Run
Gas pressure dropped below minimum during firing
Likely Causes
- Gas supply pressure dropped during firing
- Gas regulator undersized for demand
- Competing appliances drawing gas
First Checks
- Monitor gas pressure during operation
- Check gas regulator size and setting
- Verify no other appliances are consuming gas
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E128 — Stack Temperature Too High
Stack gas temperature exceeded maximum allowable limit
Likely Causes
- Fouled heat exchanger surfaces
- Recirculation of flue gases
- Excessive input rate
First Checks
- Clean heat exchanger flue passages
- Inspect venting for recirculation
- Verify input rate setting
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E130 — Ignition Failure — Trial 3
Third ignition trial failure — manual reset lockout
Likely Causes
- Gas supply problems
- Igniter electrode worn or fouled
- Gas valve malfunction
- Defective ignition transformer
First Checks
- Check gas supply and pressure
- Inspect igniter electrode
- Test gas valve
- Check ignition transformer output
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E149 — DHW Outlet Sensor Fault
DHW outlet temperature sensor open or short circuit
Likely Causes
- DHW outlet sensor wiring fault
- Defective sensor
- Loose connector
First Checks
- Check DHW outlet sensor wiring
- Measure sensor resistance
- Replace sensor
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E152 — DHW Inlet Sensor Fault
DHW inlet temperature sensor open or short circuit
Likely Causes
- DHW inlet sensor wiring fault
- Defective sensor
First Checks
- Check DHW inlet sensor wiring
- Measure sensor resistance
- Replace sensor
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E162 — Fan Speed Low During Run
Fan speed dropped below minimum during firing
Likely Causes
- Fan motor wear or failure
- Restriction in air intake or flue
- Fan speed control issue
First Checks
- Check fan speed during firing
- Inspect air inlet and flue for restriction
- Test fan motor
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E164 — Condensate System Fault
Condensate system fault detected — blocked drain or backup
Likely Causes
- Blocked condensate drain
- Frozen condensate trap
- Condensate neutralizer clogged
First Checks
- Check condensate drain for blockage
- Inspect condensate trap and neutralizer
- Check drain line slope
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E195 — Low Water Cutoff Active
Low water cutoff device has activated
Likely Causes
- System water level below minimum
- Air in system causing false LWCO trigger
- Defective LWCO device
First Checks
- Check system water level and add water if needed
- Bleed air from system
- Test LWCO device operation
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E211 — Header Sensor Fault
Header temperature sensor open or short circuit
Likely Causes
- Header sensor wiring fault
- Defective header sensor
First Checks
- Check header sensor wiring
- Measure resistance
- Replace sensor
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E214 — High Limit Circuit Open
External high limit circuit is open
Likely Causes
- Manual-reset high limit tripped
- External safety device open
- Missing wiring jumper
First Checks
- Check and manually reset high limit switch
- Inspect external safety devices
- Verify jumper if no external device
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E215 — Auxiliary Sensor 1 Fault
Auxiliary sensor 1 open or short circuit
Likely Causes
- Auxiliary sensor 1 wiring fault
- Defective sensor
First Checks
- Check aux sensor 1 wiring
- Measure resistance
- Replace sensor
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E217 — Outdoor Temperature Sensor Fault
Outdoor air temperature sensor open or short circuit
Likely Causes
- Outdoor sensor wiring damaged or exposed to weather
- Defective sensor
- Connector corrosion
First Checks
- Inspect outdoor sensor wiring for weather damage
- Measure sensor resistance
- Replace sensor and protect from weather
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E310 — BST Communication Fault
Boiler sequencing communication fault
Likely Causes
- BST network cable disconnected or damaged
- Address conflict on BST network
- Power loss to one or more BST boilers
First Checks
- Check BST network cabling between boilers
- Verify boiler addresses are unique
- Check all BST boilers are powered
Source: img1.wsimg.com
Lochinvar · SMART SYSTEM / SMART TOUCH
E316 — Modbus Communication Fault
Modbus communication fault
Likely Causes
- Modbus wiring fault
- Incorrect Modbus address or baud rate settings
- BAS not communicating
First Checks
- Check Modbus RS-485 wiring
- Verify Modbus address and communication settings
- Test BAS connection
Source: img1.wsimg.com
Weil-McLain · Ultra/Evergreen Sage control, GV90+ integrated control, Aqua-Plus/AquaBalance controller
E01 — Outlet High Temperature — Lockout
Boiler outlet water temperature exceeded the high-limit value; boiler has locked out.
Likely Causes
- Low or no water circulation
- Closed zone valve or pump failure
- Air-locked system
- Scale in heat exchanger
First Checks
- Verify pump is running
- Check all zone valves for proper operation
- Purge air from system
- Measure actual outlet temperature
Source: Weil-McLain Ultra Boiler Fault Codes PDF (img1.wsimg.com/d30153d6); heatland.ca/weil-mclain-boiler-error-codes
Weil-McLain · Ultra/Evergreen Sage control, GV90+ integrated control, Aqua-Plus/AquaBalance controller
E02 — Inlet High Temperature — Lockout
Boiler inlet water temperature exceeded the high-inlet limit, indicating return water is too hot.
Likely Causes
- Hot water bypassing back to return
- System hydraulic short-circuit
- Heat stored in buffer tank returning too hot
- Piping error
First Checks
- Check for hydraulic short circuit between supply and return
- Measure actual inlet temperature
- Review piping configuration
- Verify mixing valve if installed
Source: Weil-McLain Ultra Boiler Fault Codes PDF (img1.wsimg.com/d30153d6)
Weil-McLain · Ultra/Evergreen Sage control, GV90+ integrated control, Aqua-Plus/AquaBalance controller
E03 — No Ignition — Lockout
Boiler failed to establish a flame on 3 consecutive ignition attempts.
Likely Causes
- Gas supply off or low pressure
- Faulty igniter
- Failed flame sensor
- Gas valve not opening
First Checks
- Confirm gas supply is on and at correct pressure
- Inspect igniter for damage
- Test flame sensor
- Check gas valve for operation
Source: Weil-McLain Ultra Boiler Fault Codes PDF; heatland.ca/weil-mclain
Weil-McLain · Ultra/Evergreen Sage control, GV90+ integrated control, Aqua-Plus/AquaBalance controller
E04 — Flame Lost During Operation — Lockout
Flame lost during normal operation (not during ignition trial).
Likely Causes
- Gas supply interruption
- Combustion air issue
- Draft problems
- Failing flame sensor
First Checks
- Check gas pressure during operation
- Inspect air supply and venting
- Test flame sensor signal strength
- Check venting for backdraft
Source: Weil-McLain Ultra Boiler Fault Codes PDF (img1.wsimg.com/d30153d6)
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