CTC
CTC Furnaces Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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E01
Furnace will not start; inducer motor does not run; no ignition sequence begins.
Inducer Draft Motor Failure
E02
Furnace starts inducer but ignition does not occur; no flame is established.
Ignition Failure / Igniter Fault
E03
Furnace attempts to start but shuts down quickly; pressure switch error indicated.
Pressure Switch Not Proving Draft
E04
Furnace lights but flame goes out after a few seconds; flame failure lockout.
Flame Sensor Not Proving Flame
E05
Furnace does not respond to thermostat; control board shows thermostat input fault.
Thermostat Circuit / Low-Voltage Control Fault
E06
Furnace shuts down on high temperature; limit switch open error.
High Limit Switch Tripped / Overheat Condition
E07
Furnace control indicates rollout switch open; burners shut down immediately after ignition attempt.
Flame Rollout / Rollout Switch Trip
E08
Furnace indicates open door or cabinet switch; unit will not run.
Blower Door Safety Switch Open
E09
Furnace control shows low flame signal or unstable flame; intermittent heat.
Weak Flame Signal / Poor Grounding
E10
Furnace control indicates gas valve fault; no gas flow to burners during ignition sequence.
Gas Valve Circuit Failure
E11
Furnace indicates ignition lockout after multiple failed ignition attempts.
Ignition Lockout / Repeated Failure to Light
E12
Furnace control shows open auxiliary limit or vent temperature switch; unit shuts down mid-cycle.
Auxiliary Limit / Vent Temperature Switch Open
E13
Furnace indicates condensate overflow or blocked drain; unit shuts down to protect.
Condensate Drain Blockage
E14
Furnace control indicates reversed or missing line polarity / improper grounding.
Line Polarity / Ground Fault
E15
Furnace indicates low 24 V transformer output or control voltage fault.
Low-Voltage Transformer Failure
E16
Furnace indicates blower motor fault; blower fails to start or runs erratically.
Circulating Blower Motor Failure
E17
Furnace indicates communication error between main control board and ECM blower module.
ECM Communication Fault
E18
Furnace indicates outdoor temperature sensor fault (for models with integrated outdoor reset or dual-fuel).
Outdoor Temperature Sensor Failure
E19
Furnace indicates internal memory or configuration error on control board.
Control Board Configuration / EEPROM Fault
E20
Furnace indicates low flame rollout or vent temperature sensor wiring fault.
Safety Sensor Wiring Open/Short
Symptom
Furnace blower runs continuously even when there is no call for heat or fan.
Blower Stuck in Continuous Mode
Symptom
Furnace causes noticeable vibration and rattling in ducts and cabinet during operation.
Excessive Vibration / Loose Components
Symptom
Furnace cycles on and off rapidly with clicking from the control board but burners do not stay lit.
Intermittent Flame Sensing / Control Relay Chatter
Symptom
Furnace emits a metallic scraping or grinding noise from the blower area.
Blower Wheel Rubbing or Bearing Failure
Symptom
Furnace emits a strong burning dust smell when it first starts for the season.
Dust Burn-Off on Heat Exchanger
Symptom
Furnace frequently trips the household circuit breaker.
Overcurrent / Electrical Short
Symptom
Furnace inducer runs continuously but burners do not ignite.
Stuck Pressure Switch or Faulty Ignition Sequence
Symptom
Furnace makes loud banging or booming noise at startup.
Delayed Ignition / Burner Light-Off Noise
Symptom
Furnace occasionally emits a faint gas smell at startup near the unit.
Minor Gas Odor at Ignition
Symptom
Furnace produces a high-pitched whine or squeal during blower operation.
Blower Motor or Wheel Noise
Symptom
Furnace runs but produces insufficient heat; home never reaches set temperature.
Underheating / Low Heat Output
Symptom
Furnace runs but some rooms are too hot while others are too cold.
Uneven Heating / Airflow Imbalance
Symptom
Furnace shuts down when access panel is slightly bumped or moved.
Intermittent Door Switch or Loose Connection
Symptom
Furnace starts and runs briefly, then shuts off and restarts repeatedly (short cycling).
Short Cycling
Symptom
Furnace will not start at all; no lights or display on the control board.
No Power to Furnace
Symptom
Visible rust or water stains on or around the furnace cabinet.
Corrosion from Moisture Intrusion
Symptom
Water is leaking around the base of the furnace or inside the blower compartment (condensing models).
Condensate Leak
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E01 |
Furnace will not start; inducer motor does not run; no ignition sequence begins.
|
Inducer Draft Motor Failure | View Details |
| E02 |
Furnace starts inducer but ignition does not occur; no flame is established.
|
Ignition Failure / Igniter Fault | View Details |
| E03 |
Furnace attempts to start but shuts down quickly; pressure switch error indicated.
|
Pressure Switch Not Proving Draft | View Details |
| E04 |
Furnace lights but flame goes out after a few seconds; flame failure lockout.
|
Flame Sensor Not Proving Flame | View Details |
| E05 |
Furnace does not respond to thermostat; control board shows thermostat input fault.
|
Thermostat Circuit / Low-Voltage Control Fault | View Details |
| E06 |
Furnace shuts down on high temperature; limit switch open error.
|
High Limit Switch Tripped / Overheat Condition | View Details |
| E07 |
Furnace control indicates rollout switch open; burners shut down immediately after ignition attempt.
|
Flame Rollout / Rollout Switch Trip | View Details |
| E08 |
Furnace indicates open door or cabinet switch; unit will not run.
|
Blower Door Safety Switch Open | View Details |
| E09 |
Furnace control shows low flame signal or unstable flame; intermittent heat.
|
Weak Flame Signal / Poor Grounding | View Details |
| E10 |
Furnace control indicates gas valve fault; no gas flow to burners during ignition sequence.
|
Gas Valve Circuit Failure | View Details |
| E11 |
Furnace indicates ignition lockout after multiple failed ignition attempts.
|
Ignition Lockout / Repeated Failure to Light | View Details |
| E12 |
Furnace control shows open auxiliary limit or vent temperature switch; unit shuts down mid-cycle.
|
Auxiliary Limit / Vent Temperature Switch Open | View Details |
| E13 |
Furnace indicates condensate overflow or blocked drain; unit shuts down to protect.
|
Condensate Drain Blockage | View Details |
| E14 |
Furnace control indicates reversed or missing line polarity / improper grounding.
|
Line Polarity / Ground Fault | View Details |
| E15 |
Furnace indicates low 24 V transformer output or control voltage fault.
|
Low-Voltage Transformer Failure | View Details |
| E16 |
Furnace indicates blower motor fault; blower fails to start or runs erratically.
|
Circulating Blower Motor Failure | View Details |
| E17 |
Furnace indicates communication error between main control board and ECM blower module.
|
ECM Communication Fault | View Details |
| E18 |
Furnace indicates outdoor temperature sensor fault (for models with integrated outdoor reset or dual-fuel).
|
Outdoor Temperature Sensor Failure | View Details |
| E19 |
Furnace indicates internal memory or configuration error on control board.
|
Control Board Configuration / EEPROM Fault | View Details |
| E20 |
Furnace indicates low flame rollout or vent temperature sensor wiring fault.
|
Safety Sensor Wiring Open/Short | View Details |
| – |
Furnace blower runs continuously even when there is no call for heat or fan.
|
Blower Stuck in Continuous Mode | View Details |
| – |
Furnace causes noticeable vibration and rattling in ducts and cabinet during operation.
|
Excessive Vibration / Loose Components | View Details |
| – |
Furnace cycles on and off rapidly with clicking from the control board but burners do not stay lit.
|
Intermittent Flame Sensing / Control Relay Chatter | View Details |
| – |
Furnace emits a metallic scraping or grinding noise from the blower area.
|
Blower Wheel Rubbing or Bearing Failure | View Details |
| – |
Furnace emits a strong burning dust smell when it first starts for the season.
|
Dust Burn-Off on Heat Exchanger | View Details |
| – |
Furnace frequently trips the household circuit breaker.
|
Overcurrent / Electrical Short | View Details |
| – |
Furnace inducer runs continuously but burners do not ignite.
|
Stuck Pressure Switch or Faulty Ignition Sequence | View Details |
| – |
Furnace makes loud banging or booming noise at startup.
|
Delayed Ignition / Burner Light-Off Noise | View Details |
| – |
Furnace occasionally emits a faint gas smell at startup near the unit.
|
Minor Gas Odor at Ignition | View Details |
| – |
Furnace produces a high-pitched whine or squeal during blower operation.
|
Blower Motor or Wheel Noise | View Details |
| – |
Furnace runs but produces insufficient heat; home never reaches set temperature.
|
Underheating / Low Heat Output | View Details |
| – |
Furnace runs but some rooms are too hot while others are too cold.
|
Uneven Heating / Airflow Imbalance | View Details |
| – |
Furnace shuts down when access panel is slightly bumped or moved.
|
Intermittent Door Switch or Loose Connection | View Details |
| – |
Furnace starts and runs briefly, then shuts off and restarts repeatedly (short cycling).
|
Short Cycling | View Details |
| – |
Furnace will not start at all; no lights or display on the control board.
|
No Power to Furnace | View Details |
| – |
Visible rust or water stains on or around the furnace cabinet.
|
Corrosion from Moisture Intrusion | View Details |
| – |
Water is leaking around the base of the furnace or inside the blower compartment (condensing models).
|
Condensate Leak | View Details |
No matching codes found
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