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Error code reference

LG HVAC Error Code 4

LA09xHV/LA12xHV/LS902HPV/LS122HPV

LG codesLG hvac codes
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What the 4 error code actually means

On some LG models, this error means the outdoor unit has detected a problem with a temperature sensor inside the unit, either because the sensor has failed or the unit has overheated. On other LG models, this error means the indoor unit's drain pan is too full of water, the condensate pump that removes that water has stopped working, or a small jumper plug is missing from the control board. In any case, the system has shut itself down to prevent damage.

Diagnostic procedure

The full 4 procedure

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1
First diagnostic step
Heat sink thermistor must be 5,600Ω at 38°C/100°F & 20,700Ω at 10°C/50°F. For float switch: check drain pan is empty & pump working; if no pump, ensure blue jumper plug inserted in IDU PCB plug CN_FLOAT.
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Most common causes of 4

Ranked by how often they cause this code
  1. 1Condensate drain pan full or blocked drain
  2. 2Missing CN_FLOAT jumper plug on non-pump units
  3. 3Failed condensate pump
  4. 4Heat sink thermistor failure (LA09xHV, LA12xHV, LS902HPV, LS122HPV only)
  5. 5Outdoor unit power module overheating (LA09xHV, LA12xHV, LS902HPV, LS122HPV only)

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Questions people ask about 4

What does 4 mean on a LG hvac?
Error code 4 on LG HVAC systems means one of two things depending on the model. On LA09xHV, LA12xHV, LS902HPV, and LS122HPV units, it indicates the outdoor unit PCB heat sink thermistor has failed or the heat sink has reached 95°C. On all other LG models, it means the indoor unit condensate float switch has opened, which is typically caused by a full drain pan, a failed condensate pump, or a missing jumper plug on the indoor PCB.
Is error code 4 on a LG HVAC dangerous?
On indoor units, error code 4 is a protective shutdown to prevent water from overflowing the drain pan and causing water damage or mold growth. On outdoor units, the code protects the power electronics from heat damage. Neither condition is immediately dangerous to occupants, but the system should not be forced to run continuously while the fault is present.
Will resetting the unit clear error code 4 on a LG HVAC?
A power reset may temporarily clear the display, but the error code will return if the underlying fault is not corrected. For float switch faults, the drain pan must be emptied and the drainage system restored to proper function before the system will operate normally. For thermistor or overheating faults on the outdoor unit models, the failed component must be repaired or replaced to achieve a lasting fix.
Can I fix error code 4 on my LG HVAC myself?
Some causes of error code 4 are accessible to a knowledgeable DIYer. Clearing a blocked drain line, checking the condensate pump for operation, and verifying the blue jumper plug is seated in the CN_FLOAT connector on the indoor PCB are all reasonable first steps. Replacing the outdoor unit heat sink thermistor or diagnosing power module overheating on the affected outdoor models is more involved and may require a qualified technician.
How much does it cost to repair error code 4 on a LG HVAC?
Costs vary widely depending on the root cause. Clearing a drain line or installing a missing jumper plug may cost little to nothing if done by the homeowner. Condensate pump replacement typically runs in the range of $100 to $300 including labor. Heat sink thermistor replacement on outdoor units generally falls between $150 and $400 depending on parts availability and technician rates.

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