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
The boiler locks out with F.01 on the display, no ignition, and the status light is red.
Ignition Failure / No Flame Detected
F.02
The boiler displays F.02 and shuts down shortly after starting; the flame proves, then drops out.
Flame Loss During Operation
F.03
Boiler displays F.03 and will not fire; the fan may run briefly then stop.
Air Pressure Switch / Fan Proving Fault
F.04
Boiler locks out with F.04, no ignition; the fan may run continuously.
High Limit / Outlet Water Temperature Exceeded
F.05
Boiler displays F.05 and shuts down; this may occur intermittently during long runs.
Inlet Water Temperature Sensor Fault
F.06
Boiler displays F.06 and will not fire; this sometimes occurs after a power surge or wiring work.
Flow Switch / Low Water Flow Fault
F.07
Boiler locks out with F.07; the fan may run, but ignition does not occur.
Gas Valve / Gas Train Fault
F.08
Boiler displays F.08; this may occur during venting issues or high wind conditions.
Blocked Flue / Vent System Fault
F.09
Boiler displays F.09 and will not start; this often occurs after wiring changes or lightning.
Ignition Control / Main Control Board Fault
F.10
Boiler displays F.10; it may run at reduced output or lock out.
Supply Temperature Sensor Fault
F.11
Boiler intermittently displays F.11, especially during high demand.
Return Temperature Sensor Fault
F.12
Boiler displays F.12 and shuts down; this is 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
A strong smell of gas near the boiler, even when it is not firing.
Gas Leak in Boiler Gas Train or Piping
Symptom
Boiler cycles on and off but some zones or radiators remain cold
Zone Control / Distribution 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 operates but energy bills are unusually high compared to previous seasons
Reduced Efficiency / Condensing Not Achieved
Symptom
Boiler runs but does not heat the building adequately; radiators or air handlers are lukewarm.
Insufficient Boiler Output / Underheating
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
The boiler display is on but unresponsive; buttons do not work or respond slowly.
User Interface / Control Panel Fault
Symptom
The boiler emits an exhaust smell or flue gas odor in the mechanical room.
Flue Gas Spillage / Venting Problem
Symptom
The boiler locks out frequently during windy conditions, with no specific code displayed or only a generic lockout.
Wind-Induced Venting Issues
Symptom
The boiler makes loud banging or knocking noises when firing or shortly after.
Kettling / Boiling in Heat Exchanger
Symptom
The boiler or nearby piping vibrates excessively and produces humming or rumbling noises.
Hydronic Flow Imbalance / Pump Vibration
Symptom
The boiler pressure relief valve drips or discharges water periodically.
Overpressure / Expansion Control Problem
Symptom
The boiler runs, but domestic hot water (DHW) is not hot enough or fluctuates in temperature.
Domestic Hot Water Priority / Sensor or Valve Issue
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 |
The boiler locks out with F.01 on the display, no ignition, and the status light is red.
|
Ignition Failure / No Flame Detected | View Details |
| F.02 |
The boiler displays F.02 and shuts down shortly after starting; the flame proves, then drops out.
|
Flame Loss During Operation | View Details |
| F.03 |
Boiler displays F.03 and will not fire; the fan may run briefly then stop.
|
Air Pressure Switch / Fan Proving Fault | View Details |
| F.04 |
Boiler locks out with F.04, no ignition; the fan may run continuously.
|
High Limit / Outlet Water Temperature Exceeded | View Details |
| F.05 |
Boiler displays F.05 and shuts down; this may occur intermittently during long runs.
|
Inlet Water Temperature Sensor Fault | View Details |
| F.06 |
Boiler displays F.06 and will not fire; this sometimes occurs after a power surge or wiring work.
|
Flow Switch / Low Water Flow Fault | View Details |
| F.07 |
Boiler locks out with F.07; the fan may run, but ignition does not occur.
|
Gas Valve / Gas Train Fault | View Details |
| F.08 |
Boiler displays F.08; this may occur during venting issues or high wind conditions.
|
Blocked Flue / Vent System Fault | View Details |
| F.09 |
Boiler displays F.09 and will not start; this often occurs after wiring changes or lightning.
|
Ignition Control / Main Control Board Fault | View Details |
| F.10 |
Boiler displays F.10; it may run at reduced output or lock out.
|
Supply Temperature Sensor Fault | View Details |
| F.11 |
Boiler intermittently displays F.11, especially during high demand.
|
Return Temperature Sensor Fault | View Details |
| F.12 |
Boiler displays F.12 and shuts down; this is 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 |
| – |
A strong smell of gas near the boiler, even when it is not firing.
|
Gas Leak in Boiler Gas Train or Piping | View Details |
| – |
Boiler cycles on and off but some zones or radiators remain cold
|
Zone Control / Distribution 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 operates but energy bills are unusually high compared to previous seasons
|
Reduced Efficiency / Condensing Not Achieved | View Details |
| – |
Boiler runs but does not heat the building adequately; radiators or air handlers are lukewarm.
|
Insufficient Boiler Output / Underheating | 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 |
| – |
The boiler display is on but unresponsive; buttons do not work or respond slowly.
|
User Interface / Control Panel Fault | View Details |
| – |
The boiler emits an exhaust smell or flue gas odor in the mechanical room.
|
Flue Gas Spillage / Venting Problem | View Details |
| – |
The boiler locks out frequently during windy conditions, with no specific code displayed or only a generic lockout.
|
Wind-Induced Venting Issues | View Details |
| – |
The boiler makes loud banging or knocking noises when firing or shortly after.
|
Kettling / Boiling in Heat Exchanger | View Details |
| – |
The boiler or nearby piping vibrates excessively and produces humming or rumbling noises.
|
Hydronic Flow Imbalance / Pump Vibration | View Details |
| – |
The boiler pressure relief valve drips or discharges water periodically.
|
Overpressure / Expansion Control Problem | View Details |
| – |
The 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 |
| – |
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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