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Symptom guide / microwave
microwave: it runs but the food comes out cold
How the unit is installed decides this fault before the failed part does: a countertop microwave and a built-in one are the same symptom with opposite conclusions. What failed matters less than how the thing is installed. A countertop unit is usually not worth a repair visit at all — a completed repair runs $265–$527 [S1] against a replacement that starts around $130 — while a built-in or over-the-range unit almost always is, because the replacement has to match a cutout or a mounting. The complaint arrives in these words: runs but the food stays cold, lights up and spins but does not heat, heats weakly and takes twice as long or heats for a minute then stops heating, and the fault behind it is almost always in the high-voltage circuit rather than the controls.
high likelihoodadvanced$265–$527 installedabout 60 min
lights up and spins but does not heatruns but the food stays cold
The most frequent no-heat failure and the cheapest part: a one-way electrical valve that either works or does not, so it fails suddenly with no decline beforehand. S2 adds that it works with the capacitor to push the transformer up to roughly 4,000 volts, that a shorted diode often announces itself with a loud buzzing hum and sometimes a tripped breaker, and that it is not a DIY part. S1 deliberately publishes no per-component medians for microwaves because the sample is too small, so the figure here is its overall completed-repair range ($265-527, median $376).
the sources do not publish a per-component figure for microwaves; the cost shown is the overall completed-repair range the source does publish
high likelihoodadvanced$180–$350 installedabout 90 min
heats weakly and takes twice as long
The tube that actually produces the microwave energy. It wears out rather than failing outright, so the first sign is everything taking longer: a cup of water that took 90 seconds now takes three minutes. S2 puts an installed magnetron at $180-350, which it notes frequently exceeds the value of a countertop unit. The water test makes this measurable: one cup of cold water on full power for two minutes should come out steaming. S1's replacement line is a failed magnetron on a unit already past ten years. Time basis: no published duration, book estimate.
priced by the source as an installed replacement; no part-only figure is claimed
medium likelihoodadvanced$265–$527 installedabout 60 min
runs but the food stays cold
Produces no heat and often a humming noise. Both sources are emphatic that this is where the danger sits: the capacitor holds thousands of volts long after the unit is unplugged, sometimes for a long time, and has to be discharged deliberately with a bleeder resistor before anything inside can be touched. Contact can be fatal. Cost basis: the source publishes only the overall repair range for microwaves.
no per-component figure is published for microwaves; the cost shown is the overall completed-repair range
medium likelihoodadvanced$265–$527 installedabout 75 min
lights up and spins but does not heat
S2's tell is electrical rather than thermal: a failed transformer often trips the breaker or blows the fuse immediately when the cook cycle starts. A loud hum with cold food points at the transformer or a failing capacitor, and both draw heavily as they fail. Cost basis: the source publishes only the overall repair range for microwaves.
no per-component figure is published for microwaves; the cost shown is the overall completed-repair range
medium likelihoodadvanced$265–$527 installedabout 60 min
lights up and spins but does not heat
The safety design that stops the magnetron firing unless the door is properly closed and latched. When a latch hook wears or a switch fails, the control never receives permission to start, so the display and light work and nothing else does. A door that rattles, needs a firm push or has become loose points straight at this. S2 notes the monitor switch can also signal not-closed while the light and fan still run. Cost basis: the source publishes only the overall repair range for microwaves. Time basis: no published duration, book estimate.
no per-component figure is published for microwaves; the cost shown is the overall completed-repair range
medium likelihoodadvanced$265–$527 installedabout 60 min
runs but the food stays cold
The small mica panel on the interior side wall that protects the opening where energy enters the cavity. Once it is soiled or burnt through it arcs, and continued arcing damages the magnetron, turning a small repair into a large one. S1's instruction is to stop using the unit: sparking, a burning smell or scorch marks inside mean unplug it and have it looked at. Cost basis: the source publishes only the overall repair range for microwaves.
no per-component figure is published for microwaves; the cost shown is the overall completed-repair range
Repair or replace?
The verdict
If you can carry it, replace it. If it is bolted to the wall or built into cabinetry, repair it. A countertop unit's repair approaches the price of a new one that arrives with a full warranty; a built-in or over-the-range unit means matching a cutout or a mounting and dealing with venting, and a discontinued model can turn a swap into cabinetry work. The one exception on a built-in is a failed magnetron past ten years. [S1]
The page behind this record publishes a median and a middle half without a per-cause breakdown, and it says so itself: it does not publish a per-component median for microwaves because the sample for an individual part is too small to give a trustworthy median. That is the reason no count stands beside any cause here, and the record quotes the limit rather than filling it. The only figures the publisher attaches to this appliance are the $376 median completed repair, the $265 to $527 middle half, the $99 diagnostic applied to the repair, and its own free fixes; it also states the share of its work microwaves make up, well under one percent of completed jobs, as a share rather than as a count of this set. The replacement prices by type and the installed magnetron range are the other source's own figures, named as that source's on the page and never blended with the medians. 2026-10-31: Live measurement: S1 (Bozmanfix) continues to publish overall microwave median $380 (IQR $265-527), explicitly states no per-component medians because sample per part too small; S2 (FlexFul) provides only magnetron installed cost range $180-350, no per-component medians for other causes. No source publishes per-cause median with IQR for the not-heating symptom, so second_band cannot be added, record closes as MISS.
The installation decides this one, not the part: roughly $130 for a countertop replacement against a $265-527 repair, $450-850 plus installation over the range, and above $1,000 built in.
the source's replacement line: a failed magnetron on a unit already past ten years is the one case where replacement wins even on a built-in, because the other components are near the end of their life too. Replacement prices by type come from S2: countertop around $130, over-the-range $450-850 plus installation, built-in and drawer units above $1,000
Have a quote?
Put your quote and the age of the unit into the calculator — the same half-of-new-price rule, with your own numbers.
runs but the food stays coldlights up and spins but does not heat
The one free cause, and the source calls it the single most common no-fault reason a microwave behaves exactly like a broken one: the display lights, the turntable spins, the fan runs, the timer counts down and the magnetron never fires. It exists so retailers can run units on a shop floor, and it gets switched on accidentally by a child pressing a key sequence or by a power event. On most models you hold a specific key (commonly 1, Off or Cancel) for several seconds; the model manual gives the exact sequence. Free.
tripped thermal cutout from restricted airflow [S1]
medium likelihoodeasyno part neededabout 30 min
heats for a minute then stops heating
Heat that works and then cuts out mid-cycle is thermal protection doing its job, not a failed part: the cutout shuts the magnetron down when it exceeds a safe temperature, and on over-the-range units the usual cause is grease filters clogged with cooking residue so the fan cannot move air. Cleaning them is free; replacement filters are inexpensive and neither source prices them. S2 adds the maintenance rule: clean the grease filter monthly and replace the charcoal filter yearly on recirculating installations.
What each fix costs
Cause
Cost
Time
DIY?
demo (showroom) mode left switched on
no part needed
5 min
easy
tripped thermal cutout from restricted airflow
no part needed
30 min
easy
failed magnetron
$180–$350 installed
90 min
advanced
failed high-voltage diode
$265–$527 installed
60 min
advanced
failed high-voltage capacitor
$265–$527 installed
60 min
advanced
failed high-voltage transformer
$265–$527 installed
75 min
advanced
door interlock switches
$265–$527 installed
60 min
advanced
burnt or soiled waveguide cover (arcing)
$265–$527 installed
60 min
advanced
A technician visit starts with a diagnostic fee of $99 [S1]. Completed repairs run $265–$527 [S1].
Sources
[S1]Bozmanfix (medians from completed work orders; page updated September 2026) (2026-09). the $376 median with the middle half at $265-527 and the $99 credited diagnostic, demo mode as the free no-fault cause, the high-voltage circuit explanation, the water test, the thermal cutout and grease-filter finding, the door interlock failure, the waveguide cover and arcing warning, the carry-it-or-fix-it rule, the ten-year magnetron line and the lethal-capacitor warning
[S2]FlexFul Appliance Repair (Chicagoland) (2026-03-15). the diode's role in doubling the transformer voltage to about 4,000 volts, an installed magnetron at $180-350, the capacitor and transformer failure signatures (humming, tripped breaker), the two-minute water test, the repair maths by installation type ($130 countertop, $450-850 over the range, over $1,000 built in), and the maintenance rules (never run it empty, filters monthly and yearly)
Last verified: 2026-10-31. Prices are US market figures from the sources above; your quote may differ.
Built from a fact record, not from a template: every number above is tied to one of the sources and the record is re-checked against them. Editorial choices (which symptom leads, which cause is the single tell) are kept in a separate block so the facts stay auditable.
Quick answers
How much does it cost to fix a microwave with this problem?
Completed repairs run $265–$527 according to the sources cited on this page, after a diagnostic fee of $99.
How long does a microwave last?
The decision rule used on this page works from a planning life of 10 years.
Repair or replace?
If you can carry it, replace it. If it is bolted to the wall or built into cabinetry, repair it. A countertop unit's repair approaches the price of a new one that arrives with a full warranty; a built-in or over-the-range unit means matching a cutout or a mounting and dealing with venting, and a discontinued model can turn a swap into cabinetry work. The one exception on a built-in is a failed magnetron past ten years.
