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Error code reference

LG Microwave Error Code F5

High initial temperature of oven cavity detected (oven cavity temperature too high at start).

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High initial temperature of oven cavity detected (oven cavity temperature too high at start).

First step from the service manual

Wait until oven cavity cools to low temperature.

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
  • Wiring diagram references and connector pinouts from the OEM service manual
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What F5 means on a LG microwave

The F5 error code on an LG microwave indicates that the oven cavity temperature sensor has detected an abnormally high temperature inside the cooking chamber at the moment the unit was asked to begin a cooking cycle. Rather than allowing the magnetron to energize and add more heat to an already-overheated cavity, the control board reads the thermistor or temperature sensor signal and blocks operation as a protective measure. This prevents potential damage to internal components and reduces the risk of overheating.

The cavity temperature sensor continuously monitors the internal temperature and reports that value to the main control board. When a new cook cycle is initiated, the board checks this reading against an acceptable starting threshold. If the measured temperature exceeds that threshold, the F5 code is triggered and the unit halts. This is most commonly encountered when the microwave has been used for an extended period or run through multiple back-to-back cycles without adequate cooling time in between.

In most cases, F5 is a conditional fault rather than an indication of a failed component. The primary resolution is to open the door, allow the cavity to cool down to a normal ambient temperature, and then attempt operation again. However, if the error appears after only brief use, or if the cavity does not feel excessively warm, the temperature sensor itself may be reading inaccurately due to a fault or wiring issue, which would require further component-level diagnosis.

Source: manufacturer service documentation.

Common causes of F5

  1. 01

    Overheated cavity from consecutive use

    Wiring / connection

    Running multiple cooking cycles back-to-back without rest periods can raise the cavity temperature above the acceptable starting threshold. Allowing the unit to cool for 10 to 20 minutes typically resolves this.

  2. 02

    Blocked or restricted ventilation

    Wiring / connection

    If the microwave's air vents are obstructed by cabinetry, walls, or debris, heat cannot escape properly and the cavity temperature builds up over time. Check that all vent openings are clear and that clearance requirements around the unit are met.

  3. 03

    Faulty cavity temperature sensor or thermistor

    Part replacement

    If the sensor is defective, it may report an artificially high temperature reading even when the cavity is at normal ambient temperature. This would cause F5 to appear consistently regardless of actual heat levels, pointing to a sensor replacement.

  4. 04

    Damaged or loose sensor wiring

    Wiring / connection

    A wire connector to the temperature sensor that is loose, corroded, or pinched can cause erratic resistance readings that the control board interprets as an overtemperature condition. Inspecting and reseating the sensor harness connector may resolve this.

  5. 05

    Control board misreading sensor signal

    Part replacement

    In less common cases, the main control board itself may be misinterpreting the sensor input due to a board-level fault. If the sensor and wiring check out correctly, the control board may need evaluation or replacement.

See the test procedure for each cause

Frequently asked questions about F5

What does F5 mean on a LG microwave?
The F5 error code on an LG microwave means the control board detected that the oven cavity temperature was too high at the moment a cooking cycle was started. It is a protective fault that prevents the magnetron from operating in an already-overheated cavity. In most cases, the fix is simply allowing the unit to cool down before attempting to use it again.
How do I fix the F5 error on my LG microwave?
Start by opening the microwave door and letting the cavity cool to room temperature, which typically takes 10 to 20 minutes. Once cooled, close the door and try starting a cycle again. If the error persists after the unit is fully cooled, check that the vents are not blocked, and if the problem continues, the cavity temperature sensor or its wiring may need to be inspected and potentially replaced.
Is it safe to use my LG microwave when it shows F5?
The F5 code is actually the microwave's safety system working correctly by refusing to operate when it detects excess heat. You should not attempt to force the unit to run while this code is displayed. Wait for the cavity to cool, and if the error clears on its own, the microwave is safe to use normally. If the error appears repeatedly or does not clear after cooling, have the unit inspected before continued use.
Will resetting my LG microwave clear the F5 error?
A power reset by unplugging the unit for a few minutes may clear the code from the display, but if the underlying cause is an actually high cavity temperature, the code will return as soon as you try to start a cook cycle. The only lasting fix for a heat-related F5 is to let the cavity cool fully. If the code reappears even after the microwave is cold, a component fault such as a bad sensor is the likely cause and the reset will not resolve it.
How much does it cost to repair an LG microwave showing an F5 error?
If the issue is simply an overheated cavity, there is no repair cost at all since waiting for the unit to cool resolves the problem. If a cavity temperature sensor needs to be replaced, parts and labor costs typically range from around $75 to $200 depending on the service provider and part availability. If the main control board is at fault, repair costs can range from $150 to $350 or more, at which point comparing the repair cost to the cost of a replacement unit is worth considering.

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