Day & Night
Day & Night Furnaces Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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11
The furnace does not start at all; there is no inducer motor operation, no ignitor glow, and no blower activity. The LED flashes code 11 (no previous code stored).
Control Board Power-Up / No Fault Stored
12
The furnace attempts to start but stops; the LED shows code 12 (blower on after power-up). The blower may run briefly after power is restored.
Blower On After Power-Up / Normal Post-Power Cycle
13
The furnace shuts down, and the LED flashes code 13 (limit switch lockout). The blower may run continuously, but the burners will not light.
High Limit Switch Lockout
14
The furnace attempts ignition but locks out after several tries; the LED shows code 14 (ignition lockout). The inducer runs, the ignitor glows, but the burners fail to stay lit.
Ignition Lockout / Failed Flame Establishment
21
The furnace LED flashes code 21; the inducer may start but the burners do not light. This often indicates a gas heating lockout or a gas valve fault.
Gas Heating Lockout / Gas Valve Fault
22
The furnace LED flashes code 22; the inducer may not start or runs briefly then stops. No ignition sequence proceeds.
Inducer Motor Fault / Pressure Switch Not Proving
23
The furnace LED flashes code 23; the inducer runs but ignition does not proceed. This is often associated with a pressure switch stuck closed or open at the wrong time.
Pressure Switch Fault (Stuck Open/Closed)
24
The furnace LED flashes code 24; there is no response to the thermostat, or intermittent operation occurs. This often indicates an open or shorted secondary (24V) circuit.
24V Control Circuit Open/Short
31
The furnace LED flashes code 31; the inducer may run but the ignition sequence does not complete. This often indicates a pressure, draft, or venting problem.
Pressure Switch Did Not Close or Open Properly
32
The furnace LED flashes code 32; the blower may run unexpectedly or not at all. This indicates a low heat speed or blower fault on some Day & Night models.
Blower Motor Low Heat Speed Fault
33
The furnace LED flashes code 33; burners may light briefly then shut off, and the blower runs continuously. This indicates an open limit or rollout switch.
Limit or Flame Rollout Switch Open
34
The furnace LED flashes code 34; the ignitor may not glow or glows weakly, resulting in no burner ignition.
Ignition Proving Fault / Ignitor Failure
41
The furnace LED flashes code 41; the blower may run at an incorrect speed or not at all. This often indicates a blower motor fault (ECM or PSC).
Blower Motor Fault / Speed Error
42
Furnace LED flashes code 42. The inducer or blower may run unexpectedly, or the furnace may short-cycle. This often indicates an inducer or gas valve relay fault.
Inducer or Gas Valve Relay Stuck
43
Furnace LED flashes code 43. This indicates a pressure switch or venting problem during high-fire or low-fire operation on two-stage models.
Two-Stage Pressure Switch / Venting Fault
44
Furnace LED flashes code 44. This may indicate a flame sensing or communication fault on some advanced Day & Night models.
Flame Sensing Circuit / Communication Error
45
Furnace LED flashes code 45. The furnace may shut down and require a manual reset. This often indicates a control board lockout due to repeated faults.
Hard Lockout / Multiple Faults Detected
55
Furnace LED flashes code 55. This indicates no previous faults are stored, or the memory has been cleared.
No Stored Fault / Memory Clear
Symptom
Furnace blower continues to run for a very long time after burners shut off, blowing cool air.
Fan Off-Delay / Stuck Fan Relay
Symptom
Furnace causes strong vibration and rumbling through the ductwork when running.
Excessive Vibration / Duct Resonance
Symptom
Furnace cycles on and off very quickly (every 1–5 minutes) without reaching the thermostat setpoint.
Thermostat or Sizing-Related Short Cycling
Symptom
Furnace frequently trips the household breaker when starting or during operation.
Overcurrent / Electrical Short
Symptom
Furnace ignitor glows, but burners do not light; a faint gas smell may be present near the furnace.
No Gas Flow / Ignition Failure
Symptom
Furnace intermittently fails to start on very cold or very windy days.
Weather-Related Venting / Combustion Issues
Symptom
Furnace is very noisy during operation, producing rattling, squealing, or grinding sounds from the unit.
Mechanical Noise / Vibration
Symptom
Furnace makes a loud booming or delayed ignition noise when burners light.
Delayed Ignition
Symptom
Furnace produces unusual odors when running, such as burning dust or a metallic smell.
Odor / Contaminant Burn-Off
Symptom
Furnace runs, but some rooms are too cold while others are too warm.
Uneven Heating / Airflow Imbalance
Symptom
Furnace runs, but the carbon monoxide detector in the home alarms during operation.
Combustion / Venting Hazard
Symptom
Furnace starts normally, but shuts off when the blower comes on.
Blower-Induced Flame Disturbance / Limit Trip
Symptom
Rust or water stains visible inside the burner compartment or on the heat exchanger surfaces.
Internal Corrosion / Condensate Misrouting
Symptom
The furnace blower runs but the burners never light; cool air blows continuously.
Stuck Fan On / No Heat Call
Symptom
The furnace runs but produces no heat; the blower runs continuously, circulating room temperature air.
Burners Not Igniting / No Flame
Symptom
The furnace short cycles: burners ignite and run for 1–3 minutes, then shut off, restarting frequently.
Overheating / Limit Cycling
Symptom
The furnace starts then shuts down after a few seconds; burners light but go out quickly.
Flame Sensing Failure
Symptom
The furnace will not start at all; there are no lights, no blower, and no inducer operation.
No Power to Furnace
Symptom
Thermostat calls for heat, but the furnace only runs the inducer; burners never ignite, and no error code is visible to the homeowner.
Pressure Switch Not Closing
Symptom
Water leaking around the base of the furnace or from attached PVC pipes.
Condensate Leak (High-Efficiency Models)
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| 11 |
The furnace does not start at all; there is no inducer motor operation, no ignitor glow, and no blower activity. The LED flashes code 11 (no previous code stored).
|
Control Board Power-Up / No Fault Stored | View Details |
| 12 |
The furnace attempts to start but stops; the LED shows code 12 (blower on after power-up). The blower may run briefly after power is restored.
|
Blower On After Power-Up / Normal Post-Power Cycle | View Details |
| 13 |
The furnace shuts down, and the LED flashes code 13 (limit switch lockout). The blower may run continuously, but the burners will not light.
|
High Limit Switch Lockout | View Details |
| 14 |
The furnace attempts ignition but locks out after several tries; the LED shows code 14 (ignition lockout). The inducer runs, the ignitor glows, but the burners fail to stay lit.
|
Ignition Lockout / Failed Flame Establishment | View Details |
| 21 |
The furnace LED flashes code 21; the inducer may start but the burners do not light. This often indicates a gas heating lockout or a gas valve fault.
|
Gas Heating Lockout / Gas Valve Fault | View Details |
| 22 |
The furnace LED flashes code 22; the inducer may not start or runs briefly then stops. No ignition sequence proceeds.
|
Inducer Motor Fault / Pressure Switch Not Proving | View Details |
| 23 |
The furnace LED flashes code 23; the inducer runs but ignition does not proceed. This is often associated with a pressure switch stuck closed or open at the wrong time.
|
Pressure Switch Fault (Stuck Open/Closed) | View Details |
| 24 |
The furnace LED flashes code 24; there is no response to the thermostat, or intermittent operation occurs. This often indicates an open or shorted secondary (24V) circuit.
|
24V Control Circuit Open/Short | View Details |
| 31 |
The furnace LED flashes code 31; the inducer may run but the ignition sequence does not complete. This often indicates a pressure, draft, or venting problem.
|
Pressure Switch Did Not Close or Open Properly | View Details |
| 32 |
The furnace LED flashes code 32; the blower may run unexpectedly or not at all. This indicates a low heat speed or blower fault on some Day & Night models.
|
Blower Motor Low Heat Speed Fault | View Details |
| 33 |
The furnace LED flashes code 33; burners may light briefly then shut off, and the blower runs continuously. This indicates an open limit or rollout switch.
|
Limit or Flame Rollout Switch Open | View Details |
| 34 |
The furnace LED flashes code 34; the ignitor may not glow or glows weakly, resulting in no burner ignition.
|
Ignition Proving Fault / Ignitor Failure | View Details |
| 41 |
The furnace LED flashes code 41; the blower may run at an incorrect speed or not at all. This often indicates a blower motor fault (ECM or PSC).
|
Blower Motor Fault / Speed Error | View Details |
| 42 |
Furnace LED flashes code 42. The inducer or blower may run unexpectedly, or the furnace may short-cycle. This often indicates an inducer or gas valve relay fault.
|
Inducer or Gas Valve Relay Stuck | View Details |
| 43 |
Furnace LED flashes code 43. This indicates a pressure switch or venting problem during high-fire or low-fire operation on two-stage models.
|
Two-Stage Pressure Switch / Venting Fault | View Details |
| 44 |
Furnace LED flashes code 44. This may indicate a flame sensing or communication fault on some advanced Day & Night models.
|
Flame Sensing Circuit / Communication Error | View Details |
| 45 |
Furnace LED flashes code 45. The furnace may shut down and require a manual reset. This often indicates a control board lockout due to repeated faults.
|
Hard Lockout / Multiple Faults Detected | View Details |
| 55 |
Furnace LED flashes code 55. This indicates no previous faults are stored, or the memory has been cleared.
|
No Stored Fault / Memory Clear | View Details |
| – |
Furnace blower continues to run for a very long time after burners shut off, blowing cool air.
|
Fan Off-Delay / Stuck Fan Relay | View Details |
| – |
Furnace causes strong vibration and rumbling through the ductwork when running.
|
Excessive Vibration / Duct Resonance | View Details |
| – |
Furnace cycles on and off very quickly (every 1–5 minutes) without reaching the thermostat setpoint.
|
Thermostat or Sizing-Related Short Cycling | View Details |
| – |
Furnace frequently trips the household breaker when starting or during operation.
|
Overcurrent / Electrical Short | View Details |
| – |
Furnace ignitor glows, but burners do not light; a faint gas smell may be present near the furnace.
|
No Gas Flow / Ignition Failure | View Details |
| – |
Furnace intermittently fails to start on very cold or very windy days.
|
Weather-Related Venting / Combustion Issues | View Details |
| – |
Furnace is very noisy during operation, producing rattling, squealing, or grinding sounds from the unit.
|
Mechanical Noise / Vibration | View Details |
| – |
Furnace makes a loud booming or delayed ignition noise when burners light.
|
Delayed Ignition | View Details |
| – |
Furnace produces unusual odors when running, such as burning dust or a metallic smell.
|
Odor / Contaminant Burn-Off | View Details |
| – |
Furnace runs, but some rooms are too cold while others are too warm.
|
Uneven Heating / Airflow Imbalance | View Details |
| – |
Furnace runs, but the carbon monoxide detector in the home alarms during operation.
|
Combustion / Venting Hazard | View Details |
| – |
Furnace starts normally, but shuts off when the blower comes on.
|
Blower-Induced Flame Disturbance / Limit Trip | View Details |
| – |
Rust or water stains visible inside the burner compartment or on the heat exchanger surfaces.
|
Internal Corrosion / Condensate Misrouting | View Details |
| – |
The furnace blower runs but the burners never light; cool air blows continuously.
|
Stuck Fan On / No Heat Call | View Details |
| – |
The furnace runs but produces no heat; the blower runs continuously, circulating room temperature air.
|
Burners Not Igniting / No Flame | View Details |
| – |
The furnace short cycles: burners ignite and run for 1–3 minutes, then shut off, restarting frequently.
|
Overheating / Limit Cycling | View Details |
| – |
The furnace starts then shuts down after a few seconds; burners light but go out quickly.
|
Flame Sensing Failure | View Details |
| – |
The furnace will not start at all; there are no lights, no blower, and no inducer operation.
|
No Power to Furnace | View Details |
| – |
Thermostat calls for heat, but the furnace only runs the inducer; burners never ignite, and no error code is visible to the homeowner.
|
Pressure Switch Not Closing | View Details |
| – |
Water leaking around the base of the furnace or from attached PVC pipes.
|
Condensate Leak (High-Efficiency Models) | View Details |
No matching codes found
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