Lochinvar Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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F.01
Boiler locks out with F.01 on display, no ignition, status light red
Ignition Failure / No Flame Detected
F.02
Boiler displays F.02 and shuts down shortly after starting, flame proves then drops out
Flame Loss During Operation
F.03
Boiler shows F.03 and will not fire, fan may run briefly then stop
Air Pressure Switch / Fan Proving Fault
F.04
Boiler locks out with F.04, no ignition, fan may run continuously
High Limit / Outlet Water Temperature Exceeded
F.05
Boiler displays F.05 and shuts down, may occur intermittently during long runs
Inlet Water Temperature Sensor Fault
F.06
Boiler shows F.06, will not fire, sometimes after power surge or wiring work
Flow Switch / Low Water Flow Fault
F.07
Boiler locks out with F.07, fan may run but ignition does not occur
Gas Valve / Gas Train Fault
F.08
Boiler shows F.08, may occur during venting issues or high wind conditions
Blocked Flue / Vent System Fault
F.09
Boiler displays F.09, will not start, often after wiring changes or lightning
Ignition Control / Main Control Board Fault
F.10
Boiler shows F.10, may run at reduced output or lock out
Supply Temperature Sensor Fault
F.11
Boiler intermittently shows F.11, especially during high demand
Return Temperature Sensor Fault
F.12
Boiler shows F.12 and shuts down, often associated with very hot return water
Return Temperature Too High / Delta-T Fault
F.13
Boiler displays F.13, often during very cold weather or long vent runs
Combustion Air / Intake Blockage Fault
F.14
Boiler shows F.14 and will not fire, may occur after control replacement
Configuration / Parameter Error
F.15
Boiler intermittently shows F.15, especially when multiple zones call
Low Water Pressure / System Fill Fault
F.16
Boiler shows F.16 and shuts down, often with very high temperature readings
Overheat / Safety Thermostat Trip
F.17
Boiler displays F.17, may still operate but with limited modulation
Fan Speed / Combustion Blower Fault
F.18
Boiler shows F.18, often associated with condensate issues
Condensate Drain Fault
F.19
Boiler intermittently shows F.19, especially when outdoor reset is enabled
Outdoor Temperature Sensor Fault
F.20
Boiler shows F.20 and locks out, often immediately on a call for heat
Low Voltage / Power Supply Fault
Symptom
Boiler cycles on and off but some zones or radiators remain cold
Zone Control / Distribution Problem
Symptom
Boiler display is on but unresponsive, buttons do not work or respond slowly
User Interface / Control Panel Fault
Symptom
Boiler emits exhaust smell or flue gas odor in the mechanical room
Flue Gas Spillage / Venting Problem
Symptom
Boiler frequently locks out with generic flame failure but no specific F-code shown on basic models
Intermittent Flame Sensing Problem
Symptom
Boiler frequently reaches setpoint very quickly and shuts off, with very hot supply but cool returns
Low System Flow / Piping Restriction
Symptom
Boiler ignites with a loud boom or delayed ignition noise
Delayed Ignition / Improper Light-off
Symptom
Boiler locks out frequently during windy conditions, with no specific code displayed or only generic lockout
Wind-Induced Venting Issues
Symptom
Boiler makes loud banging or knocking noises when firing or shortly after
Kettling / Boiling in Heat Exchanger
Symptom
Boiler operates but energy bills are unusually high compared to previous seasons
Reduced Efficiency / Condensing Not Achieved
Symptom
Boiler or nearby piping vibrates excessively and produces humming or rumbling noises
Hydronic Flow Imbalance / Pump Vibration
Symptom
Boiler pressure relief valve drips or discharges water periodically
Overpressure / Expansion Control Problem
Symptom
Boiler runs but does not heat the building adequately, radiators or air handlers are lukewarm
Insufficient Boiler Output / Underheating
Symptom
Boiler runs but domestic hot water (DHW) is not hot enough or fluctuates in temperature
Domestic Hot Water Priority / Sensor or Valve Issue
Symptom
Boiler short cycles, turning on and off frequently with small temperature changes
Short Cycling / Control Oversensitivity
Symptom
Boiler will not start, display is blank, no lights or response
No Power to Boiler
Symptom
Strong smell of gas near the boiler, even when it is not firing
Gas Leak in Boiler Gas Train or Piping
Symptom
Visible corrosion or rust streaks on or inside the boiler cabinet
Chronic Condensation / Leak-Induced Corrosion
Symptom
Water leaking from under the boiler cabinet or from piping connections
System Leak / Internal Boiler Leak
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| F.01 |
Boiler locks out with F.01 on display, no ignition, status light red
|
Ignition Failure / No Flame Detected | View Details |
| F.02 |
Boiler displays F.02 and shuts down shortly after starting, flame proves then drops out
|
Flame Loss During Operation | View Details |
| F.03 |
Boiler shows F.03 and will not fire, fan may run briefly then stop
|
Air Pressure Switch / Fan Proving Fault | View Details |
| F.04 |
Boiler locks out with F.04, no ignition, fan may run continuously
|
High Limit / Outlet Water Temperature Exceeded | View Details |
| F.05 |
Boiler displays F.05 and shuts down, may occur intermittently during long runs
|
Inlet Water Temperature Sensor Fault | View Details |
| F.06 |
Boiler shows F.06, will not fire, sometimes after power surge or wiring work
|
Flow Switch / Low Water Flow Fault | View Details |
| F.07 |
Boiler locks out with F.07, fan may run but ignition does not occur
|
Gas Valve / Gas Train Fault | View Details |
| F.08 |
Boiler shows F.08, may occur during venting issues or high wind conditions
|
Blocked Flue / Vent System Fault | View Details |
| F.09 |
Boiler displays F.09, will not start, often after wiring changes or lightning
|
Ignition Control / Main Control Board Fault | View Details |
| F.10 |
Boiler shows F.10, may run at reduced output or lock out
|
Supply Temperature Sensor Fault | View Details |
| F.11 |
Boiler intermittently shows F.11, especially during high demand
|
Return Temperature Sensor Fault | View Details |
| F.12 |
Boiler shows F.12 and shuts down, often associated with very hot return water
|
Return Temperature Too High / Delta-T Fault | View Details |
| F.13 |
Boiler displays F.13, often during very cold weather or long vent runs
|
Combustion Air / Intake Blockage Fault | View Details |
| F.14 |
Boiler shows F.14 and will not fire, may occur after control replacement
|
Configuration / Parameter Error | View Details |
| F.15 |
Boiler intermittently shows F.15, especially when multiple zones call
|
Low Water Pressure / System Fill Fault | View Details |
| F.16 |
Boiler shows F.16 and shuts down, often with very high temperature readings
|
Overheat / Safety Thermostat Trip | View Details |
| F.17 |
Boiler displays F.17, may still operate but with limited modulation
|
Fan Speed / Combustion Blower Fault | View Details |
| F.18 |
Boiler shows F.18, often associated with condensate issues
|
Condensate Drain Fault | View Details |
| F.19 |
Boiler intermittently shows F.19, especially when outdoor reset is enabled
|
Outdoor Temperature Sensor Fault | View Details |
| F.20 |
Boiler shows F.20 and locks out, often immediately on a call for heat
|
Low Voltage / Power Supply Fault | View Details |
| – |
Boiler cycles on and off but some zones or radiators remain cold
|
Zone Control / Distribution Problem | View Details |
| – |
Boiler display is on but unresponsive, buttons do not work or respond slowly
|
User Interface / Control Panel Fault | View Details |
| – |
Boiler emits exhaust smell or flue gas odor in the mechanical room
|
Flue Gas Spillage / Venting Problem | View Details |
| – |
Boiler frequently locks out with generic flame failure but no specific F-code shown on basic models
|
Intermittent Flame Sensing Problem | View Details |
| – |
Boiler frequently reaches setpoint very quickly and shuts off, with very hot supply but cool returns
|
Low System Flow / Piping Restriction | View Details |
| – |
Boiler ignites with a loud boom or delayed ignition noise
|
Delayed Ignition / Improper Light-off | View Details |
| – |
Boiler locks out frequently during windy conditions, with no specific code displayed or only generic lockout
|
Wind-Induced Venting Issues | View Details |
| – |
Boiler makes loud banging or knocking noises when firing or shortly after
|
Kettling / Boiling in Heat Exchanger | View Details |
| – |
Boiler operates but energy bills are unusually high compared to previous seasons
|
Reduced Efficiency / Condensing Not Achieved | View Details |
| – |
Boiler or nearby piping vibrates excessively and produces humming or rumbling noises
|
Hydronic Flow Imbalance / Pump Vibration | View Details |
| – |
Boiler pressure relief valve drips or discharges water periodically
|
Overpressure / Expansion Control Problem | View Details |
| – |
Boiler runs but does not heat the building adequately, radiators or air handlers are lukewarm
|
Insufficient Boiler Output / Underheating | View Details |
| – |
Boiler runs but domestic hot water (DHW) is not hot enough or fluctuates in temperature
|
Domestic Hot Water Priority / Sensor or Valve Issue | View Details |
| – |
Boiler short cycles, turning on and off frequently with small temperature changes
|
Short Cycling / Control Oversensitivity | View Details |
| – |
Boiler will not start, display is blank, no lights or response
|
No Power to Boiler | View Details |
| – |
Strong smell of gas near the boiler, even when it is not firing
|
Gas Leak in Boiler Gas Train or Piping | View Details |
| – |
Visible corrosion or rust streaks on or inside the boiler cabinet
|
Chronic Condensation / Leak-Induced Corrosion | View Details |
| – |
Water leaking from under the boiler cabinet or from piping connections
|
System Leak / Internal Boiler Leak | View Details |
No matching codes found
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