Michael Thompson Key Takeaways
- LG microwave F-1 means an open thermistor — the temperature sensor has stopped reporting a reading entirely.
- LG microwave F-1 worth repairing in most cases — the thermistor is one of the least expensive parts on the appliance.
- Built-in and over-the-range models favor repair even more strongly, since replacement adds reinstallation cost.
- F-1 is far cheaper to fix than a magnetron or high-voltage circuit fault, which look similar to owners but cost very differently.
- Diagnostic work starts from $89, and the repair is typically completed in the same visit.
The Bottom Line
LG microwave F-1 worth repairing in nearly every case — the thermistor is an inexpensive, well-defined fix, and replacing a built-in unit over this one fault rarely makes financial sense.
Yes, in most cases. An LG microwave that trips its own safety cutoff and posts F-1 is reporting an open thermistor, and this specific fault is one of the least expensive on the appliance's whole code list to put right.
| Factor | What it means for the decision |
|---|---|
| Thermistor replacement cost | Low relative to most microwave repairs |
| Microwave age under 8 years | Repair — straightforward sensor swap |
| Multiple other faults present | Weigh against a new unit |
| Built-in or over-the-range model | Repair favored — replacement means reinstallation cost too |
What Does the LG Microwave F-1 Code Mean?
F-1 means the thermistor — the sensor that monitors the temperature inside the cooking cavity — has an open circuit and is no longer reporting a reading at all. This is different from a sensor reading incorrectly; an open thermistor reports nothing, and the control responds by refusing to run rather than operating on a guess about the cavity temperature.
This safety-first behavior is deliberate. A microwave that ran without any temperature feedback at all would have no way to prevent an overheating condition inside the cavity, so the control treats "no reading" as a reason to stop rather than a detail to work around. That is a good thing from a safety standpoint, and it is also good news from a cost standpoint — it means the fault is caught early, before it can damage anything else inside the unit, such as the magnetron or the cavity liner.
Is an LG Microwave F-1 Worth Repairing?
Yes, in most cases, and more clearly so than many other microwave faults. A thermistor is a small, inexpensive part, and the labor to replace it is modest compared to jobs that involve the magnetron or the high-voltage circuit — the more expensive components on this appliance. This is exactly the kind of narrow, single-part fault where repairing makes more sense than replacing the whole unit, especially on a built-in or over-the-range model, where replacement carries an installation cost on top of the appliance price that a countertop model would not.
- Microwave under 8 years old with only F-1 showing: repair — this is a low-cost, well-defined fix.
- Built-in or over-the-range model: repair is favored even more strongly, since replacement adds reinstallation cost.
- F-1 alongside other faults like arcing, a failing turntable motor, or door switch issues: get a full diagnostic before deciding, since the combined cost may shift the balance.
- Microwave well past 10 years old with multiple issues: weigh the combined repair cost against a new unit's price and installation.
How F-1 Compares to Other Microwave Faults
Our broader LG microwave error codes guide covers the full range of faults this appliance can post, and F-1 sits toward the inexpensive end of that list. A magnetron failure or a high-voltage capacitor fault, by contrast, involves both a pricier part and more involved labor, and those are the faults where the repair-versus-replace math looks different. Knowing which end of that range your specific code falls on is the difference between booking a repair with confidence and wondering whether it was worth it afterward.
- Confirm the exact code before assuming cost — F-1 and a magnetron fault look similar from the outside but cost very differently to fix.
- Ask for the part identified specifically during a diagnostic visit, not just "a sensor issue," so you know exactly what is being replaced.
- Compare the quote to a new unit's price including installation if yours is built-in.
- Factor in downtime — a sensor repair is typically a same-visit fix, while a full replacement usually means a wait for the new unit and a second visit to install it.
What an F-1 Repair Costs
Diagnostic work on an LG microwave sensor fault starts from $89, and a confirmed thermistor replacement is one of the least expensive repairs on this appliance's whole fault list. The exact total is confirmed in writing once the part is identified. Keeping the vents around a built-in or over-the-range unit clear, covered in our LG microwave vent care guide, also helps prevent heat-related sensor faults like this one from developing in the first place.
Our LG microwave repair service covers the thermistor, door switches, and turntable assembly together in one visit. Schedule a visit or describe the code you saw to get a clear answer before committing to either repair or replacement.
What If You Are Not Sure of the Exact Code?
Write down exactly what the display shows before calling, including any dashes or spacing — LG's own microwave codes distinguish between similar-looking faults, and a code copied slightly wrong can send a technician in with the wrong part in hand. If the display is blank or unreadable, note what happened right before the fault appeared instead, such as a long cook cycle or a recent cleaning with the door open, since that context also helps narrow down the likely cause ahead of the visit.
A microwave that has been reliable for years and then suddenly shows F-1 has not necessarily reached the end of its service life — a thermistor can fail on its own schedule regardless of how well the rest of the unit has held up, much like a light bulb failing in an otherwise sound fixture. This is part of why the repair-versus-replace math favors repair so clearly here: the fault is isolated to one small, inexpensive component rather than being a symptom of the whole appliance wearing out together. Owners weighing a replacement purely because a repair feels like "giving up" on an older unit are often surprised to learn just how affordable this specific fix is once they see it broken out from the appliance's other, pricier possible faults.
- Write the code exactly as shown, including any hyphen or spacing, before calling.
- Note the last thing cooked and for how long, in case the fault relates to a specific heavy-use cycle.
- Check whether the microwave still powers on at all — a completely dead unit points at a different fault than one that powers on but refuses to start a cycle.
- Mention if this is a repeat occurrence of the same code, since a thermistor that has failed once rarely fails only partially.
It is worth not confusing F-1 with its close neighbor, F-2, a shorted thermistor rather than an open one. Both involve the same sensor and cost roughly the same to fix, but they describe opposite electrical failures — F-1 reports no signal at all, while F-2 reports a signal that is stuck or invalid because the circuit has shorted. The distinction rarely changes what an owner should do, which is book a diagnostic either way, but it does help a technician predict what they will find before the cover ever comes off.
Our F-1 code page itself lists the exact wording LG uses for this fault, which is worth comparing against what your display shows before assuming the diagnosis.