--- title: "Microwave not heating" description: "LG microwave not heating: one of the most specific symptoms in this trade. Everything else about the machine works — the turntable turns, the fan runs, the…" url: "https://lgmiami.support/symptoms/microwave-not-heating/" date_modified: "2026-09-05" Appliance type: "Microwaves" --- # LG microwave not heating ### The one-cup test Put a plain glass or mug with about a cup of cold water in the middle of the cavity and run the machine on full for one minute. Water that is noticeably warm afterwards means the microwave is producing power and the complaint is about time or quantity rather than the machine. Water that is exactly as cold as it went in confirms the diagnosis, and it takes a minute. ### What it usually means, by the kind of LG appliance LG sells one appliance in several forms — five shapes of washer, three kinds of dryer, four fuels of range — and the same behavior points at different things on each of them. A built-in side-by-side and an integrated column are not the same service situation, and a dual-fuel range and an induction range fail in different halves. - **Over the range** — Worth repairing nearly always, because the installation, the trim and the ventilation are part of what you paid for. - **Countertop** — The honest arithmetic often favors replacement, and we will say so. - **Combination wall oven** — Definitely worth repairing — the microwave is half of a built-in cabinet and cannot be swapped for a countertop machine. ### Why nothing else being wrong is the diagnosis A microwave has two nearly independent halves: the machinery you can see — turntable, light, fan, controls — and the high-voltage circuit that actually cooks. The first runs on ordinary mains and the second on several thousand volts produced by a transformer, a capacitor, a diode and the magnetron. So a machine where everything visible works perfectly and nothing heats is not a mystery. It is the second half, and only the second half. ### The honest arithmetic On a countertop machine, the parts and the labor together often approach the price of a new one, and we will tell you that rather than sell you a repair that does not make sense. On an over-the-range machine or the microwave half of a combination wall oven it is different: you are not just buying a microwave, you are buying the cabinet, the trim, the ventilation and the fit — and repairing is nearly always the right answer. The magnetron The part that makes the microwaves. It fails, and there is no partial version of it. The high voltage diode or capacitor Cheaper than the magnetron and produce exactly the same symptom. The transformer Less common, and it usually announces itself with a smell. A door interlock in a partial state Some interlock arrangements will let the machine run and inhibit the magnetron. Run the one-cup test A minute, a mug and cold water. It settles the question. Listen for the hum A working magnetron circuit is audible under the fan. Silence where a hum should be is informative. Check nothing is on the door seal A door not closing fully is a different and much cheaper problem. Do not open the case The capacitor in a microwave holds a lethal charge long after it is unplugged. This is the one appliance we ask people not to open. It runs, the light is on, and nothing gets hot What it usually means The magnetron circuit: magnetron, diode, capacitor or transformer Nothing else in the machine has to be wrong for this to happen On a built-in or over-the-range unit repair is usually right; on a countertop it may not be The one-cup test Put a plain glass or mug with about a cup of cold water in the middle of the cavity and run the machine on full for one minute. Water that is noticeably warm afterwards means the microwave is producing power and the complaint is about time or quantity rather than the machine. Water that is exactly as cold as it went in confirms the diagnosis, and it takes a minute. What it usually means, by the kind of LG appliance LG sells one appliance in several forms — five shapes of washer, three kinds of dryer, four fuels of range — and the same behavior points at different things on each of them. A built-in side-by-side and an integrated column are not the same service situation, and a dual-fuel range and an induction range fail in different halves. Over the range — Worth repairing nearly always, because the installation, the trim and the ventilation are part of what you paid for. Countertop — The honest arithmetic often favors replacement, and we will say so. Combination wall oven — Definitely worth repairing — the microwave is half of a built-in cabinet and cannot be swapped for a countertop machine. Why nothing else being wrong is the diagnosis A microwave has two nearly independent halves: the machinery you can see — turntable, light, fan, controls — and the high-voltage circuit that actually cooks. The first runs on ordinary mains and the second on several thousand volts produced by a transformer, a capacitor, a diode and the magnetron. So a machine where everything visible works perfectly and nothing heats is not a mystery. It is the second half, and only the second half. The honest arithmetic On a countertop machine, the parts and the labor together often approach the price of a new one, and we will tell you that rather than sell you a repair that does not make sense. On an over-the-range machine or the microwave half of a combination wall oven it is different: you are not just buying a microwave, you are buying the cabinet, the trim, the ventilation and the fit — and repairing is nearly always the right answer. ### Is it dangerous to keep using it? A machine that runs and does not heat is not leaking anything — it is producing nothing. The danger in a microwave is the reverse case: a door that does not seal or an interlock that has failed. What is dangerous is opening the case, because the capacitor stores a charge that can be lethal weeks after it was unplugged. ### It heats slowly rather than not at all. That is usually not the magnetron, which tends to work or not. Slow heating is more often low supply voltage, an overloaded circuit, or simply a machine of a lower wattage than the last one. Worth measuring before anything is replaced. --- **[Read full article: Microwave not heating](https://lgmiami.support/symptoms/microwave-not-heating/)**