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Error code reference

LG Refrigerator Error Code F2+F4

Poor defrosting at upper compartment

LG codesLG refrigerator codes

Poor defrosting at upper compartment - defrosting sensor did not reach above 7°C (16°C for GR-J213) within 2 hours after starting defrost.

First step from the service manual

Check temperature fuse, heater continuity, drain for clogging, and heater driving relay.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What F2+F4 means on a LG refrigerator

The F2+F4 error code on an LG refrigerator indicates a defrost failure in the upper compartment. Specifically, the defrost sensor failed to reach a temperature above 7°C (or 16°C on GR-J213 models) within a 2-hour defrost cycle window. This threshold exists to confirm that the defrost heater is generating enough heat to clear frost accumulation from the evaporator coils. When the sensor does not detect this minimum temperature rise, the control board logs the fault and triggers the combined F2+F4 code to alert the technician that defrosting is incomplete or not occurring at all.

The defrost system in the upper compartment involves several components working together: a defrost heater, a temperature-sensing defrost sensor, a thermal fuse (also called a temperature fuse), and a heater driving relay on the control board. If any of these components fail, the heater may not activate or may not sustain adequate heat output during the defrost cycle. A failed thermal fuse will cut power to the heater entirely, while a faulty relay may fail to close the circuit. A defective heater element will produce no heat even if all control signals are correct.

A clogged or frozen drain is another common contributor. When the defrost drain is blocked, meltwater backs up and refreezes around the evaporator, creating an insulating ice mass that prevents the heater from raising the sensor temperature to the required threshold within the allotted time. This scenario can trigger the fault even when the heater and fuse are functioning correctly. Diagnosing this code correctly requires checking the thermal fuse for continuity, testing heater resistance, inspecting the drain for obstruction, and verifying that the heater driving relay is switching properly.

Source: manufacturer service documentation.

Common causes of F2+F4

  1. 01

    Failed Thermal (Temperature) Fuse

    Part replacement

    The thermal fuse is a one-time safety device that permanently opens if it detects excessive heat. A blown fuse cuts all power to the defrost heater, preventing any defrost cycle from completing. Test the fuse with a multimeter for continuity, as a blown fuse will read open.

  2. 02

    Defective Defrost Heater

    Part replacement

    The defrost heater element itself may have burned out or developed an open circuit. Check the heater for continuity with a multimeter. No continuity means the element needs replacement and cannot generate heat regardless of control signals.

  3. 03

    Clogged or Frozen Defrost Drain

    Wiring / connection

    A blocked drain causes meltwater to refreeze around the evaporator coils, building up an insulating ice layer. This prevents the heater from raising the compartment temperature to the required threshold within the 2-hour window, triggering the fault even when heater components are intact.

  4. 04

    Faulty Heater Driving Relay

    Part replacement

    The heater driving relay on the control board closes the circuit to activate the defrost heater. If the relay fails to switch, the heater receives no power during the defrost cycle. Inspect the relay for proper operation and check for any visible signs of burning or damage on the board.

  5. 05

    Failed Defrost Sensor

    Part replacement

    If the defrost sensor itself is malfunctioning, it may not accurately report the compartment temperature to the control board, causing the system to log a defrost failure even when the heater is operating normally. Verify sensor resistance values are within the expected range for the measured temperature.

See the test procedure for each cause

Frequently asked questions about F2+F4

What does F2+F4 mean on a LG refrigerator?
The F2+F4 code means the upper compartment defrost cycle failed to reach the required minimum temperature (above 7°C, or 16°C on GR-J213 models) within 2 hours. This indicates that the defrost heater system is not working correctly. The fault can stem from a blown thermal fuse, a failed heater element, a malfunctioning relay, or a clogged drain.
Can I fix the F2+F4 error myself?
Some causes, like a clogged defrost drain, can be cleared by a knowledgeable DIYer after unplugging the refrigerator and carefully thawing and removing the blockage. However, testing the thermal fuse, heater continuity, and heater driving relay requires a multimeter and comfort working with electrical components. Replacing a control board relay is best handled by a qualified technician.
Will resetting the refrigerator clear the F2+F4 error?
Unplugging the refrigerator and restoring power may temporarily clear the code from the display, but the fault will return if the underlying problem is not repaired. The control board triggers the code based on sensor data from the defrost cycle, so the root cause must be addressed to prevent the error from reappearing.
Is the F2+F4 error on my LG refrigerator a safety concern?
The fault itself is not an immediate safety hazard, but leaving it unresolved will cause progressive ice buildup on the evaporator coils in the upper compartment. This will reduce cooling efficiency, potentially compromise food safety, and can eventually cause the compressor to overwork. Addressing the issue promptly prevents more costly secondary damage.
How much does it cost to repair the F2+F4 error on an LG refrigerator?
Repair costs vary depending on the failed component. A thermal fuse or defrost heater replacement is typically a lower-cost repair, often in the range of $100 to $250 including parts and labor. If the control board or heater driving relay requires replacement, costs can range from $200 to $400 or more. Getting a diagnostic inspection first helps narrow down the exact part needed before committing to a repair.

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