LG F1 fault codewhat it means and how to fix it
LG publish this as a problem with the mainboard and say it requires service. There is no owner remedy, and the useful question is whether the appliance is worth it.
Take care
Get a qualified appliance engineer to look at your LG F1
We do not pass enquiries to a repair firm, so there is no form here. When you book a qualified appliance engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What F1 means
LG’s entire published text for F1 is that it "indicates a problem with the mainboard" and that the code "will require service to resolve". That is short, and it is honest in a way the longer third-party versions are not: the mainboard is the appliance’s controller, it has no user-serviceable elements, and there is no test an owner can run that would tell them anything more than the code already has. What makes F1 worth a page anyway is that the diagnosis is unusually final, and that changes the decision in front of you.
Most microwave faults have a cheap branch and an expensive branch, and the useful thing a page can do is help you find out which one you are on. F1 has only the expensive branch. So the question stops being what is wrong and becomes whether to repair it, and that turns on three things. What the appliance is: a countertop microwave is a commodity, and a board plus a visit is frequently within sight of a new one, whereas a built-in has to match a housing and the arithmetic reverses. How old it is: a mainboard failure on an appliance under two years old is a warranty matter and should cost you nothing. And whether anything else is marginal: a board on an appliance whose door already sits badly or whose turntable already grinds is money spent on the first of several repairs.
One caution about identification. There is an LG oven fault code table in circulation, published by a parts distributor rather than by LG, in which F1 means an open oven temperature sensor. If your appliance is an oven rather than a microwave you are reading the wrong page, and the two tables do not agree.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Mainboard component or track failure | The literal published meaning. Something on the controller has failed and the appliance has stopped rather than run on a fault. | Common |
| Surge damage from the supply | A spike on the ring main can take out a board outright, and a microwave shares its circuit with whatever else is in the kitchen. | Occasional |
| Long-term heat and moisture exposure | Boards sited above the cavity in a poorly ventilated housing age faster, and solder joints fail before components do. | Occasional |
| A connector rather than the board | An engineer will check the looms first, because a board reporting itself faulty sometimes turns out to be one that cannot see something. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£90–£190
Time on site
1 hour
A mainboard with a visit is typically £90 to £190 depending on model and whether the part is still stocked. Free inside the warranty period, and on a countertop appliance often more than a replacement is worth.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related LG fault codes
- F3Get it checkedLG document this one twice and differently. One article says wipe the touch panel, the other says the control panel is faulty and needs service.Related: controls and electronics
- E10Get it checkedLG say an internal short was detected in the control board, and then give you something to try anyway: unplug it for a full minute.Related: controls and electronics
- LOCUsually simple to fixNot a fault. LOC is LG’s child lock, and it releases by holding STOP/CLEAR until the display drops it.Related: same brand
- DOORGet it checkedThe word DOOR rather than a number. LG say the door is not closed or the latch is not engaged, and they include transit packing as a cause.Related: same brand
- F16Get it checkedLG say a heating issue was detected. They publish F19 with word-for-word identical text, so both codes land here.Related: same brand
- F2Get it checkedLG describe a thermistor problem putting the temperature in the unit out of range. It is the reading that is wrong, not necessarily the cavity.Related: same brand
Own a LG microwave? Save it and its codes come first next time.
Related guides
Common questions about LG F1
Is there anything at all I can try?
Run LG’s standard power cycle once — unplug it, plug it back in, see whether F1 returns. They ask for that on every F code and it costs nothing. If the code comes back, LG’s answer is service and there is no second attempt to make.
Should I repair it or replace it?
Depends on the appliance more than the fault. A countertop microwave is usually not worth a board plus a visit. A built-in usually is, because replacing it means matching the aperture and trim you already have, and that is often more expensive than the repair.
It is eighteen months old.
Then start with LG rather than an independent engineer. A mainboard failure inside the warranty period is exactly what the warranty is for, and going elsewhere first can complicate the claim.
A repair site lists F1 as an oven sensor fault.
That is from an LG oven table, not the microwave one, and it is published by a parts distributor rather than by LG. F1 and F2 mean different things in the two lists. Make sure you are matching your appliance and not just the letter and number.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.