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Error code reference

LG Refrigerator Error Code F dH

Poor defrosting

LG codesLG refrigerator codes

Poor defrosting — defrost heater error; if defrosting sensor has not exceeded 46°F (8°C) after 1 hour of defrosting, caused by temperature fuse disconnection, heater disconnection, drain jam, or poor relay for heater.

First step from the service manual

Check the door gasket for damage, then check the defrost control part (Fuse-M resistance and defrost sensor resistance).

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

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  • Step-by-step tests with expected resistance, voltage, and continuity values
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What F dH means on a LG refrigerator

The F dH error code on an LG refrigerator indicates a defrost heater failure, specifically triggered when the defrost cycle fails to raise the evaporator sensor temperature above 46°F (8°C) within one hour of active defrosting. The defrost system relies on a heater element to melt frost accumulation off the evaporator coils, with a thermistor-based sensor monitoring the temperature rise to confirm the cycle is working. When that threshold is not reached in the allotted time, the control board logs this fault and halts the defrost cycle to prevent unsafe operation.

The most common hardware causes include a blown thermal fuse (Fuse-M), which is a one-time safety device that opens permanently if the heater circuit overheats, or a physically disconnected or burned-out defrost heater element itself. A failed relay on the control board that governs the heater circuit can also prevent current from reaching the heater entirely. Additionally, a jammed or frozen drain can cause ice to back up and insulate the sensor area, preventing accurate temperature readings and triggering the fault even if the heater is partially functional.

Diagnosis should begin with a visual inspection of the door gasket, since a damaged seal allows warm, humid air to enter continuously and overload the defrost system with excessive frost. After confirming the gasket is intact, the next step is measuring resistance values on the Fuse-M thermal fuse and the defrost sensor. An open thermal fuse will read infinite resistance rather than a low value, and a faulty defrost sensor will read outside its expected resistance range for the current temperature. These readings confirm which component has failed before any parts are replaced.

Source: manufacturer service documentation.

Common causes of F dH

  1. 01

    Blown thermal fuse (Fuse-M)

    Part replacement

    The Fuse-M is a one-time thermal cutoff device in the defrost heater circuit. If it has blown due to overheating, it will read infinite resistance on a multimeter and must be replaced before the defrost heater can receive power.

  2. 02

    Defrost heater disconnection or failure

    Part replacement

    The heater element itself may be broken, burned out, or have a loose wiring connection. A working heater should show measurable continuity, while an open circuit indicates the element has failed.

  3. 03

    Failed defrost sensor

    Part replacement

    The defrost thermistor monitors temperature rise during the defrost cycle. If it reads outside its expected resistance range, the control board may incorrectly conclude the cycle has failed even when the heater is operating.

  4. 04

    Clogged or frozen defrost drain

    Wiring / connection

    A jammed drain allows ice and water to accumulate around the sensor, preventing it from registering an accurate temperature rise. Clearing the drain blockage and melting any ice buildup around the drain tube often resolves this issue.

  5. 05

    Damaged door gasket

    Part replacement

    A worn or torn door gasket allows warm, humid air into the freezer compartment continuously, causing excessive frost buildup that overwhelms the defrost system. Inspect the gasket for cracks, tears, or areas that do not seal flat against the door frame.

See the test procedure for each cause

Frequently asked questions about F dH

What does F dH mean on a LG refrigerator?
The F dH code means the refrigerator detected a defrost heater error. Specifically, the defrost cycle ran for a full hour but the evaporator sensor temperature never exceeded 46°F (8°C), which is the threshold that confirms successful defrosting. The fault is typically caused by a blown thermal fuse, a failed heater element, a bad defrost sensor, a clogged drain, or a faulty heater relay on the control board.
Can I fix the F dH error myself, or do I need a technician?
Some causes, like a frozen defrost drain or a damaged door gasket, can be addressed by a knowledgeable DIYer with basic tools. However, diagnosing and replacing internal components like the thermal fuse, defrost heater, or defrost sensor requires a multimeter and comfort working around refrigerator wiring. If you are not familiar with appliance diagnostics, a licensed technician is the safer option.
Is it safe to keep using the refrigerator when F dH is displayed?
Continuing to use the refrigerator with an active F dH error is not recommended for extended periods. Without a functioning defrost cycle, frost will accumulate on the evaporator coils and eventually block airflow entirely, causing the refrigerator and freezer sections to lose cooling capacity. Food safety can become a concern if temperatures rise enough.
Will resetting the refrigerator clear the F dH error code?
Unplugging the refrigerator or resetting the control board may temporarily clear the displayed code, but the underlying fault will remain. The error will return once the next defrost cycle runs and the same failure condition is detected. The root cause, whether a failed fuse, heater, or sensor, must be diagnosed and corrected for the code to stay cleared.
How much does it cost to repair an F dH error on an LG refrigerator?
Repair costs vary depending on which component has failed. Replacement parts such as a thermal fuse or defrost sensor are generally in the range of $10 to $50, while a defrost heater assembly can cost $30 to $100 or more. If a technician is needed for diagnosis and labor, total repair costs typically range from $100 to $300 depending on your location and the parts required.

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