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Error code reference

LG Refrigerator Error Code FZ-DEF-HEATER Error

Defrost system in freezer compartment has error (heater separation, contact error, disconnection, short…

LG codesLG refrigerator codes

Defrost system in freezer compartment has error (heater separation, contact error, disconnection, short circuit, or temperature fuse error).

First step from the service manual

With MAIN PCB CN70 and CN71 disconnected, measure resistance between CN70 White and CN71 Orange; should be 63 (230) ohm ±7%.

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

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  • Wiring diagram references and connector pinouts from the OEM service manual
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What FZ-DEF-HEATER Error means on a LG refrigerator

The FZ-DEF-HEATER error on an LG refrigerator indicates a fault within the freezer compartment's defrost heating system. This code is triggered when the control board detects an abnormality in the defrost heater circuit, which can include physical separation of the heater element, a poor or broken electrical contact, a complete wire disconnection, a short circuit condition, or a blown thermal (temperature) fuse. The defrost heater is a critical component that periodically melts frost buildup from the evaporator coils, allowing the refrigerator to maintain proper airflow and cooling efficiency.

The primary diagnostic procedure involves disconnecting connectors CN70 and CN71 from the main PCB and measuring the resistance across the CN70 White wire and the CN71 Orange wire. For a properly functioning defrost heater circuit, the resistance reading should fall at 63 ohms for 115V systems or 230 ohms for 230V systems, with an acceptable tolerance of plus or minus 7%. A reading that falls significantly outside this range, or an open circuit reading, confirms a fault within the heater element or its associated wiring and thermal fuse. A short circuit reading near zero ohms points toward insulation breakdown or a shorted heater element.

Because this error covers multiple failure modes, systematic component isolation is essential. The thermal fuse is a common failure point and acts as a one-time-use safety device that opens permanently if the defrost circuit overheats. The heater element itself can also burn out or develop a break in the resistive wire. Wiring harness integrity between the main PCB connectors and the heater assembly should also be inspected for corrosion, pinching, or loose terminals before replacing components.

Source: manufacturer service documentation.

Common causes of FZ-DEF-HEATER Error

  1. 01

    Blown Thermal (Temperature) Fuse

    Part replacement

    The thermal fuse is a one-time safety device that permanently opens if the defrost circuit overheats. A blown fuse will produce an open circuit reading during resistance testing and the fuse must be replaced.

  2. 02

    Defrost Heater Element Failure

    Part replacement

    The resistive heating element inside the freezer can burn out or develop a break, resulting in a resistance reading outside the specified 63 or 230 ohm range. This will require replacement of the heater assembly.

  3. 03

    Wiring Harness Disconnection or Damage

    Wiring / connection

    Loose terminals, corroded connectors, or pinched wiring between the main PCB connectors CN70 and CN71 and the heater assembly can interrupt the circuit. Inspect the full harness length and connector contacts before replacing parts.

  4. 04

    Poor Connector Contact at CN70 or CN71

    Wiring / connection

    Oxidation or physical loosening of the CN70 White or CN71 Orange connector terminals on the main PCB can create intermittent or complete circuit failures. Reseating and cleaning the connectors may resolve the fault.

  5. 05

    Short Circuit in Defrost Heater Circuit

    Part replacement

    Insulation breakdown on the heater element or wiring can cause a short circuit, producing a resistance reading near zero ohms. This typically requires replacement of the heater assembly and inspection of surrounding wiring.

See the test procedure for each cause

Frequently asked questions about FZ-DEF-HEATER Error

What does FZ-DEF-HEATER Error mean on a LG refrigerator?
The FZ-DEF-HEATER error indicates a fault in the freezer compartment's defrost heating system. The control board has detected an issue such as a heater disconnection, short circuit, contact error, or blown thermal fuse. This system is responsible for periodically melting frost off the evaporator coils to keep the refrigerator cooling correctly. Diagnosis requires resistance testing at the main PCB connectors CN70 and CN71.
Can I fix the FZ-DEF-HEATER error myself?
A knowledgeable DIYer can perform the initial resistance test by disconnecting CN70 and CN71 from the main PCB and measuring between the White and Orange wires, looking for a reading of 63 or 230 ohms within 7% tolerance. If the thermal fuse or heater element is confirmed faulty, replacing these parts requires accessing the freezer evaporator panel, which involves removing shelving and covers. If you are not comfortable working with refrigerator internals or interpreting electrical resistance readings, a qualified technician is recommended.
Is it safe to continue using my refrigerator when the FZ-DEF-HEATER error is displayed?
Continued use with this error active is not recommended for long periods. Without a functioning defrost heater, frost will accumulate on the evaporator coils, eventually blocking airflow and causing the refrigerator and freezer compartments to lose cooling ability. Food safety can be compromised if temperatures rise above safe levels. Address the error as soon as possible to avoid food spoilage.
How much does it cost to repair the FZ-DEF-HEATER error on an LG refrigerator?
Repair costs depend on which component has failed. A thermal fuse replacement is typically the least expensive repair, with parts generally ranging from $5 to $25 and labor adding $75 to $150 depending on your area. A defrost heater element replacement usually costs between $20 and $80 for the part, plus labor. If the main PCB is involved, costs can rise considerably higher.
Will resetting my LG refrigerator clear the FZ-DEF-HEATER error?
A power reset may temporarily clear the error code from the display, but it will not resolve the underlying electrical fault in the defrost heater circuit. The code will return once the control board runs its diagnostics again. A physical component failure such as a blown thermal fuse or broken heater element must be repaired or replaced before the error will clear permanently.

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