Laars
Laars Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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AF
Boiler displays AF or Air Flow Fault; unit will not fire or shuts down shortly after starting the fan.
Combustion Airflow Fault
AFS
Boiler displays AFS or Air Flow Switch Fault; unit will not fire.
Air Flow Switch / Proving Switch Fault
COM
Boiler displays COM or Communication Error; may affect cascade or remote control operation.
Communication Bus Fault
COND
Boiler displays COND or Condensate Fault; unit may shut down due to blocked condensate.
Condensate Drain Blockage
E01
Boiler displays E01; ignition or flame failure depending on model.
General Ignition / Flame Failure Error
E02
Boiler displays E02; often associated with high limit or overheat on some Laars controls.
High Limit or Overheat Error
E03
Boiler displays E03; commonly related to flue or exhaust sensor on some Laars models.
Flue Temperature or Exhaust Sensor Error
E04
Boiler displays E04; often indicates low water pressure or flow on some Laars controls.
Low Water Pressure / Flow Error
FAN
Boiler displays FAN or Fan Failure; inducer does not start or stops unexpectedly.
Inducer Fan / Blower Failure
FL
Boiler displays FL or Flame Loss and shuts down during or shortly after ignition.
Flame Loss During Operation
FLUE
Boiler displays FLUE or Flue Temp High; unit may derate or shut down.
Excessive Flue Gas Temperature
GAS
Boiler displays GAS or Gas Fault; unit will not fire.
Gas Supply or Gas Valve Fault
HARD
Boiler displays HARD or Hard Lockout; unit will not restart until manually reset and underlying fault persists.
Hard Safety Lockout
HL
Boiler shuts down and displays HL or High Limit; burner will not fire until reset.
High Limit Temperature Lockout
HLP
Boiler displays HLP or High Pressure; relief valve may drip or discharge water.
High System Water Pressure Condition
IGN
Boiler displays IGN or Ignition Failure; burner does not light and unit locks out after several tries.
Ignition Failure Lockout
IGN-L
Boiler displays IGN-L or Ignition Lockout; multiple failed ignition attempts.
Repeated Ignition Failure Lockout
LOC
Display shows LOC and boiler will not respond to thermostat calls or button presses.
Control Panel Child Lock / Local Lockout Active
LOP
Boiler displays LOP or Low Pressure; unit will not fire or shuts down.
Low System Water Pressure Lockout
OF
Boiler displays OF or Overheat Fault; unit locks out and may require manual reset.
Heat Exchanger Overheat / Outlet Temperature Exceeded Limit
OUT
Boiler displays OUT or Outdoor Sensor Error; outdoor reset function not working correctly.
Outdoor Temperature Sensor Fault
PS
Boiler displays PS or Pressure Switch Open; fan may run but burner does not light.
Air Proving Pressure Switch Open
PUMP
Boiler displays PUMP or Pump Fault; circulator does not run when there is a call for heat.
System Circulator Pump Failure
ROL
Boiler displays ROL or Rollout; burner shuts down and may require manual reset of rollout switch.
Flame Rollout Safety Trip
SEN
Boiler displays SEN or Sensor Error; may indicate supply, return, or flue sensor fault.
Temperature Sensor Failure or Out-of-Range Reading
SFL
Boiler displays SFL or Soft Lockout; unit stops firing but may restart after a delay or reset.
Soft Lockout Due to Repeated Ignition or Flame Failures
TSTAT
Boiler displays TSTAT or Thermostat Error; boiler does not respond to room thermostat.
Thermostat Input Fault
Symptom
Boiler cabinet or nearby area is unusually hot to the touch, even when not firing.
Standby Overheating / Poor Ventilation
Symptom
Boiler cycles on and off but domestic hot water from the Laars combi boiler is not hot enough or fluctuates.
Domestic Hot Water Temperature Instability
Symptom
Boiler frequently locks out during very cold or very windy weather but runs normally otherwise.
Weather-Related Venting / Combustion Instability
Symptom
Boiler makes gurgling or bubbling sounds inside the unit or in nearby piping.
Air in System / Microboiling
Symptom
Boiler makes loud banging or knocking noises in the piping when starting or stopping.
Water Hammer / Thermal Expansion Noise
Symptom
Boiler or flue area smells strongly of exhaust or flue gases.
Flue Gas Spillage / Venting Problem
Symptom
Boiler or nearby piping emits a whistling or high-pitched noise during operation.
Flow Restriction or Gas Flow Noise
Symptom
Boiler runs but does not heat the house adequately; radiators or baseboards are lukewarm.
Insufficient Heat Output / Underheating
Symptom
Boiler runs but radiators are hot only at the top or only some zones heat properly.
Air Binding / Zoning Imbalance
Symptom
Boiler short cycles, turning on and off frequently with very short run times.
Short Cycling Operation
Symptom
Boiler will not start at all; display is blank and no lights or sounds are present.
No Power to Boiler
Symptom
Water is dripping from the pressure relief valve discharge pipe.
Relief Valve Discharge
Symptom
Water is leaking from the bottom of the Laars boiler cabinet.
Internal Boiler Water Leak
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| AF |
Boiler displays AF or Air Flow Fault; unit will not fire or shuts down shortly after starting the fan.
|
Combustion Airflow Fault | View Details |
| AFS |
Boiler displays AFS or Air Flow Switch Fault; unit will not fire.
|
Air Flow Switch / Proving Switch Fault | View Details |
| COM |
Boiler displays COM or Communication Error; may affect cascade or remote control operation.
|
Communication Bus Fault | View Details |
| COND |
Boiler displays COND or Condensate Fault; unit may shut down due to blocked condensate.
|
Condensate Drain Blockage | View Details |
| E01 |
Boiler displays E01; ignition or flame failure depending on model.
|
General Ignition / Flame Failure Error | View Details |
| E02 |
Boiler displays E02; often associated with high limit or overheat on some Laars controls.
|
High Limit or Overheat Error | View Details |
| E03 |
Boiler displays E03; commonly related to flue or exhaust sensor on some Laars models.
|
Flue Temperature or Exhaust Sensor Error | View Details |
| E04 |
Boiler displays E04; often indicates low water pressure or flow on some Laars controls.
|
Low Water Pressure / Flow Error | View Details |
| FAN |
Boiler displays FAN or Fan Failure; inducer does not start or stops unexpectedly.
|
Inducer Fan / Blower Failure | View Details |
| FL |
Boiler displays FL or Flame Loss and shuts down during or shortly after ignition.
|
Flame Loss During Operation | View Details |
| FLUE |
Boiler displays FLUE or Flue Temp High; unit may derate or shut down.
|
Excessive Flue Gas Temperature | View Details |
| GAS |
Boiler displays GAS or Gas Fault; unit will not fire.
|
Gas Supply or Gas Valve Fault | View Details |
| HARD |
Boiler displays HARD or Hard Lockout; unit will not restart until manually reset and underlying fault persists.
|
Hard Safety Lockout | View Details |
| HL |
Boiler shuts down and displays HL or High Limit; burner will not fire until reset.
|
High Limit Temperature Lockout | View Details |
| HLP |
Boiler displays HLP or High Pressure; relief valve may drip or discharge water.
|
High System Water Pressure Condition | View Details |
| IGN |
Boiler displays IGN or Ignition Failure; burner does not light and unit locks out after several tries.
|
Ignition Failure Lockout | View Details |
| IGN-L |
Boiler displays IGN-L or Ignition Lockout; multiple failed ignition attempts.
|
Repeated Ignition Failure Lockout | View Details |
| LOC |
Display shows LOC and boiler will not respond to thermostat calls or button presses.
|
Control Panel Child Lock / Local Lockout Active | View Details |
| LOP |
Boiler displays LOP or Low Pressure; unit will not fire or shuts down.
|
Low System Water Pressure Lockout | View Details |
| OF |
Boiler displays OF or Overheat Fault; unit locks out and may require manual reset.
|
Heat Exchanger Overheat / Outlet Temperature Exceeded Limit | View Details |
| OUT |
Boiler displays OUT or Outdoor Sensor Error; outdoor reset function not working correctly.
|
Outdoor Temperature Sensor Fault | View Details |
| PS |
Boiler displays PS or Pressure Switch Open; fan may run but burner does not light.
|
Air Proving Pressure Switch Open | View Details |
| PUMP |
Boiler displays PUMP or Pump Fault; circulator does not run when there is a call for heat.
|
System Circulator Pump Failure | View Details |
| ROL |
Boiler displays ROL or Rollout; burner shuts down and may require manual reset of rollout switch.
|
Flame Rollout Safety Trip | View Details |
| SEN |
Boiler displays SEN or Sensor Error; may indicate supply, return, or flue sensor fault.
|
Temperature Sensor Failure or Out-of-Range Reading | View Details |
| SFL |
Boiler displays SFL or Soft Lockout; unit stops firing but may restart after a delay or reset.
|
Soft Lockout Due to Repeated Ignition or Flame Failures | View Details |
| TSTAT |
Boiler displays TSTAT or Thermostat Error; boiler does not respond to room thermostat.
|
Thermostat Input Fault | View Details |
| – |
Boiler cabinet or nearby area is unusually hot to the touch, even when not firing.
|
Standby Overheating / Poor Ventilation | View Details |
| – |
Boiler cycles on and off but domestic hot water from the Laars combi boiler is not hot enough or fluctuates.
|
Domestic Hot Water Temperature Instability | View Details |
| – |
Boiler frequently locks out during very cold or very windy weather but runs normally otherwise.
|
Weather-Related Venting / Combustion Instability | View Details |
| – |
Boiler makes gurgling or bubbling sounds inside the unit or in nearby piping.
|
Air in System / Microboiling | View Details |
| – |
Boiler makes loud banging or knocking noises in the piping when starting or stopping.
|
Water Hammer / Thermal Expansion Noise | View Details |
| – |
Boiler or flue area smells strongly of exhaust or flue gases.
|
Flue Gas Spillage / Venting Problem | View Details |
| – |
Boiler or nearby piping emits a whistling or high-pitched noise during operation.
|
Flow Restriction or Gas Flow Noise | View Details |
| – |
Boiler runs but does not heat the house adequately; radiators or baseboards are lukewarm.
|
Insufficient Heat Output / Underheating | View Details |
| – |
Boiler runs but radiators are hot only at the top or only some zones heat properly.
|
Air Binding / Zoning Imbalance | View Details |
| – |
Boiler short cycles, turning on and off frequently with very short run times.
|
Short Cycling Operation | View Details |
| – |
Boiler will not start at all; display is blank and no lights or sounds are present.
|
No Power to Boiler | View Details |
| – |
Water is dripping from the pressure relief valve discharge pipe.
|
Relief Valve Discharge | View Details |
| – |
Water is leaking from the bottom of the Laars boiler cabinet.
|
Internal Boiler Water Leak | View Details |
No matching codes found
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