Thermia
Thermia 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, no burner ignition, display shows E01 shortly after a call for heat.
Ignition Failure Lockout
E02
Furnace attempts to start but shuts down quickly, display shows E02, inducer may run briefly.
Pressure Switch Open / Draft Failure
E03
Burners ignite but shut off within a few seconds, furnace retries and then locks out with E03.
Flame Detection Failure
E04
Furnace display shows E04 and shuts down; high temperature limit trips during or shortly after burner operation.
High Limit Switch Open / Overheat Condition
E05
Furnace display shows E05, burners do not light, you may hear a click from the gas valve but no flame.
Gas Valve or Gas Supply Fault
E06
Furnace display shows E06, unit will not start, control board LEDs may indicate a communication error.
Control Board Communication Failure
E07
Furnace display shows E07, inducer may start but system quickly shuts down before ignition.
Combustion Air Proving Fault
E08
Furnace display shows E08, blower may run continuously without heat, or system may not respond to thermostat.
Low Voltage / Power Supply Fault
E09
Furnace display shows E09, unit may shut down unexpectedly during operation, sometimes accompanied by a burning smell.
Blower Motor Overcurrent / Overload
E10
Furnace display shows E10, unit may lock out after several failed ignition attempts, sometimes with delayed or rough ignition.
Delayed Ignition / Burner Ignition Fault
E11
Furnace display shows E11, unit may start but shuts down with a condensate-related alarm, especially on high-efficiency Thermia models.
Condensate Drain Fault
E12
Furnace display shows E12, unit may not respond to thermostat changes or may cycle erratically.
Thermostat Input Fault
E13
Furnace display shows E13, blower runs but burners do not light, often after a power outage or surge.
Internal Control Board Fault
E14
Furnace display shows E14, unit may shut down on very cold days, sometimes with long run times before fault.
Rollout Switch / Flame Rollout Fault
E15
Furnace display shows E15, unit may short-cycle or shut down with a low temperature or freeze protection alarm (often on Thermia hybrid or hydronic-integrated furnaces).
Low Water Temperature / Hydronic Loop Fault
E16
Furnace display shows E16, unit may lock out with an intake/exhaust configuration error after installation or venting changes.
Venting Configuration / Polarity Fault
E17
Furnace display shows E17, unit may run but with reduced capacity or may lock out in extreme temperatures.
Outdoor Temperature Sensor Fault (if equipped)
E18
Furnace display shows E18, unit may shut down with a safety alarm related to combustion quality.
Flue Gas / Combustion Sensor Fault
E19
Furnace display shows E19, unit may not start or may shut down when an accessory (humidifier, HRV, etc.) is active.
Accessory Control Fault
E20
Furnace display shows E20, unit may operate only at low stage or may not modulate correctly (on modulating Thermia furnaces).
Gas Valve Modulation / Step Fault
Symptom
Furnace blower runs continuously even when there is no call for heat or fan from the thermostat.
Continuous Fan Operation
Symptom
Furnace causes a noticeable increase in dust or soot around supply registers.
Sooting / Contaminated Airflow
Symptom
Furnace does not start at all; no blower, no inducer, no display or LEDs.
No Power / Dead Furnace
Symptom
Furnace emits a burning dust smell when it starts, especially at the beginning of the heating season.
Burning Dust Odor
Symptom
Furnace emits a strong metallic or electrical burning smell during operation.
Electrical Overheating / Component Failure
Symptom
Furnace frequently locks out and must be manually reset at the power switch to restart.
Repeated Safety Lockouts
Symptom
Furnace inducer runs but main blower never starts, causing the furnace to overheat and shut down.
Blower Motor Start Failure
Symptom
Furnace is very noisy in the flue or vent pipes, with whistling or roaring sounds.
Vent Noise / Resonance
Symptom
Furnace makes loud banging or booming noises at startup.
Delayed Ignition / Burner Explosion Noise
Symptom
Furnace produces a chemical or plastic smell when running.
Foreign Material on Heat Exchanger or Ducts
Symptom
Furnace produces a high-pitched whine or screeching noise during operation.
Blower or Inducer Bearing Failure
Symptom
Furnace runs but produces no heat; blower operates, but supply air is cool or only slightly warm.
No Heat with Blower Running
Symptom
Furnace runs but some rooms are too cold while others are too warm.
Uneven Heating / Poor Air Distribution
Symptom
Furnace runs but trips the household circuit breaker intermittently.
Overcurrent / Electrical Short
Symptom
Furnace short cycles, turning on and off frequently without reaching the thermostat setpoint.
Short Cycling
Symptom
Furnace starts and then shuts down within a minute, with the blower running only briefly.
Ignition or Flame Sustain Failure without Display Code
Symptom
Furnace vibrates excessively or rattles when running.
Excessive Vibration / Mechanical Rattle
Symptom
Thermostat calls for heat but furnace does not respond; no inducer or blower activity, yet control board has power.
No Call for Heat Recognized
Symptom
Water is leaking from the base of the furnace or nearby piping.
Water Leak from Condensing Furnace
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E01 |
Furnace will not start, no burner ignition, display shows E01 shortly after a call for heat.
|
Ignition Failure Lockout | View Details |
| E02 |
Furnace attempts to start but shuts down quickly, display shows E02, inducer may run briefly.
|
Pressure Switch Open / Draft Failure | View Details |
| E03 |
Burners ignite but shut off within a few seconds, furnace retries and then locks out with E03.
|
Flame Detection Failure | View Details |
| E04 |
Furnace display shows E04 and shuts down; high temperature limit trips during or shortly after burner operation.
|
High Limit Switch Open / Overheat Condition | View Details |
| E05 |
Furnace display shows E05, burners do not light, you may hear a click from the gas valve but no flame.
|
Gas Valve or Gas Supply Fault | View Details |
| E06 |
Furnace display shows E06, unit will not start, control board LEDs may indicate a communication error.
|
Control Board Communication Failure | View Details |
| E07 |
Furnace display shows E07, inducer may start but system quickly shuts down before ignition.
|
Combustion Air Proving Fault | View Details |
| E08 |
Furnace display shows E08, blower may run continuously without heat, or system may not respond to thermostat.
|
Low Voltage / Power Supply Fault | View Details |
| E09 |
Furnace display shows E09, unit may shut down unexpectedly during operation, sometimes accompanied by a burning smell.
|
Blower Motor Overcurrent / Overload | View Details |
| E10 |
Furnace display shows E10, unit may lock out after several failed ignition attempts, sometimes with delayed or rough ignition.
|
Delayed Ignition / Burner Ignition Fault | View Details |
| E11 |
Furnace display shows E11, unit may start but shuts down with a condensate-related alarm, especially on high-efficiency Thermia models.
|
Condensate Drain Fault | View Details |
| E12 |
Furnace display shows E12, unit may not respond to thermostat changes or may cycle erratically.
|
Thermostat Input Fault | View Details |
| E13 |
Furnace display shows E13, blower runs but burners do not light, often after a power outage or surge.
|
Internal Control Board Fault | View Details |
| E14 |
Furnace display shows E14, unit may shut down on very cold days, sometimes with long run times before fault.
|
Rollout Switch / Flame Rollout Fault | View Details |
| E15 |
Furnace display shows E15, unit may short-cycle or shut down with a low temperature or freeze protection alarm (often on Thermia hybrid or hydronic-integrated furnaces).
|
Low Water Temperature / Hydronic Loop Fault | View Details |
| E16 |
Furnace display shows E16, unit may lock out with an intake/exhaust configuration error after installation or venting changes.
|
Venting Configuration / Polarity Fault | View Details |
| E17 |
Furnace display shows E17, unit may run but with reduced capacity or may lock out in extreme temperatures.
|
Outdoor Temperature Sensor Fault (if equipped) | View Details |
| E18 |
Furnace display shows E18, unit may shut down with a safety alarm related to combustion quality.
|
Flue Gas / Combustion Sensor Fault | View Details |
| E19 |
Furnace display shows E19, unit may not start or may shut down when an accessory (humidifier, HRV, etc.) is active.
|
Accessory Control Fault | View Details |
| E20 |
Furnace display shows E20, unit may operate only at low stage or may not modulate correctly (on modulating Thermia furnaces).
|
Gas Valve Modulation / Step Fault | View Details |
| – |
Furnace blower runs continuously even when there is no call for heat or fan from the thermostat.
|
Continuous Fan Operation | View Details |
| – |
Furnace causes a noticeable increase in dust or soot around supply registers.
|
Sooting / Contaminated Airflow | View Details |
| – |
Furnace does not start at all; no blower, no inducer, no display or LEDs.
|
No Power / Dead Furnace | View Details |
| – |
Furnace emits a burning dust smell when it starts, especially at the beginning of the heating season.
|
Burning Dust Odor | View Details |
| – |
Furnace emits a strong metallic or electrical burning smell during operation.
|
Electrical Overheating / Component Failure | View Details |
| – |
Furnace frequently locks out and must be manually reset at the power switch to restart.
|
Repeated Safety Lockouts | View Details |
| – |
Furnace inducer runs but main blower never starts, causing the furnace to overheat and shut down.
|
Blower Motor Start Failure | View Details |
| – |
Furnace is very noisy in the flue or vent pipes, with whistling or roaring sounds.
|
Vent Noise / Resonance | View Details |
| – |
Furnace makes loud banging or booming noises at startup.
|
Delayed Ignition / Burner Explosion Noise | View Details |
| – |
Furnace produces a chemical or plastic smell when running.
|
Foreign Material on Heat Exchanger or Ducts | View Details |
| – |
Furnace produces a high-pitched whine or screeching noise during operation.
|
Blower or Inducer Bearing Failure | View Details |
| – |
Furnace runs but produces no heat; blower operates, but supply air is cool or only slightly warm.
|
No Heat with Blower Running | View Details |
| – |
Furnace runs but some rooms are too cold while others are too warm.
|
Uneven Heating / Poor Air Distribution | View Details |
| – |
Furnace runs but trips the household circuit breaker intermittently.
|
Overcurrent / Electrical Short | View Details |
| – |
Furnace short cycles, turning on and off frequently without reaching the thermostat setpoint.
|
Short Cycling | View Details |
| – |
Furnace starts and then shuts down within a minute, with the blower running only briefly.
|
Ignition or Flame Sustain Failure without Display Code | View Details |
| – |
Furnace vibrates excessively or rattles when running.
|
Excessive Vibration / Mechanical Rattle | View Details |
| – |
Thermostat calls for heat but furnace does not respond; no inducer or blower activity, yet control board has power.
|
No Call for Heat Recognized | View Details |
| – |
Water is leaking from the base of the furnace or nearby piping.
|
Water Leak from Condensing Furnace | View Details |
No matching codes found
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