--- title: "Microwave Runs but Food Stays Cold: Causes and Fixes" description: "A microwave not heating still does everything else: the light comes on, the turntable turns, the fan hums and the timer counts down, and the plate comes out as…" url: "https://microwaverepair.center/problems/microwave-not-heating/" --- # Microwave Runs but Food Stays Cold A microwave not heating still does everything else: the light comes on, the turntable turns, the fan hums and the timer counts down, and the plate comes out as cold as it went in or barely warm at the rim. ## What it usually means. Heating is the job of one chain behind the control panel. The board closes a relay, the high-voltage transformer steps household current up to a few thousand volts, the diode and capacitor double it, and the magnetron turns it into the energy aimed down the waveguide. The light, the fan and the turntable motor run on ordinary voltage, which is why a microwave can look fully alive and heat nothing. The usual failures along the chain are the magnetron, the diode, the capacitor, the transformer, a thermal cutout on the magnetron that has opened, and a door switch that feeds only the high-voltage side. A microwave that heats weakly rather than not at all can have a tired magnetron, a power level left low, or a kitchen circuit sagging while other appliances run. Two settings imitate the failure and cost nothing: a demo or showroom mode that runs the display and turntable without heating, and a power level set to 10 or 20 percent. Every part of the high-voltage chain sits behind the outer case, where the capacitor keeps its charge, so the owner's test is a cup of water and nothing further. The 7 causes, cheapest first Answer these first 01 Does a cup of water heated on full power for one minute come out hot, a little warm, or unchanged? 02 Does the hum sound the way it always has, or quieter, or louder with a buzz? 03 Does the display show full power, and is there any sign of a demo or showroom mode? 04 Did it stop heating suddenly, after a spark, a bang or an empty run, or fade over months? 05 On a speed or convection model, does it brown in convection or broil mode but not heat in microwave mode? ## Check these before you book. Microwave not heating: 5 checks, and none of them costs anything. 01 Heat one cup of water on full power for one minute; a working microwave leaves it clearly hot, not lukewarm. 02 Check that the power level reads full and that no demo or showroom sign shows, and switch demo off as the manual describes. 03 Stop using it if it sparked, banged or smelled of burning before it stopped heating. ### Also worth checking - Clear the vents: pull a countertop unit a few inches from the wall and make sure nothing covers the grille of a hood combination. - Tell us what the cup of water did and the model number from the label inside the door frame. ### How soon does it need a visit? Not urgent unless it came with a spark, a bang or a burning smell. Please do not run it empty to listen for the hum; an empty run can finish off a weak magnetron. Leave the outer case closed, because the capacitor inside keeps its charge after unplugging. ## The causes, cheapest first. 7 things microwave runs but food stays cold turns out to be, from demo mode or a low power level to browning works, microwave mode does not. [The cost guide](https://microwaverepair.center/cost/) 1. 01 no repair ### Demo mode or a low power level A store demo setting runs everything but the magnetron, and a power level set low after a defrost stays set on some models. The manual shows the keypress that ends demo mode and how to return to full power. No repair: check it yourself 2. 02 no repair ### A busy countertop circuit sagging A countertop microwave on the same circuit as a kettle, a toaster or a coffee machine can lose enough voltage to heat noticeably slower while they run. Try it with the others off. No repair: check it yourself [On a countertop microwave](https://microwaverepair.center/types/countertop-microwave-repair/) 3. 03 low to moderate ### A door switch on the high-voltage side Some models route the high-voltage side through a switch of its own. When that one stops closing, the unit runs, counts and turns, but never heats. [Fixed by microwave door switch and latch repair](https://microwaverepair.center/services/microwave-door-switch-and-latch-repair/) 4. 04 low to moderate ### Magnetron cutout opened from trapped heat Blocked vents above a hood combination's door, a trim kit without its openings clear, or a countertop unit shoved against the backsplash can trap heat until the cutout on the magnetron opens. It may heat again after cooling; if it stays open, the cutout is replaced and the airflow fixed. [Fixed by microwave magnetron repair](https://microwaverepair.center/services/microwave-magnetron-repair/) 5. 05 moderate ### High-voltage diode or capacitor failed A diode that has opened or a capacitor that has lost its value leaves the magnetron without the voltage it needs. A louder, rougher hum with no heat is typical, and both are tested with the capacitor safely discharged on a visit. [Fixed by microwave high-voltage diode and capacitor repair](https://microwaverepair.center/services/microwave-high-voltage-diode-and-capacitor-repair/) 6. 06 moderate to highest ### Magnetron worn out or failed Age, empty runs and blocked cooling wear a magnetron down until it heats weakly and then not at all. On a built-in, drawer or hood combination the repair is usually worth it; on a small countertop unit we compare it with a replacement first. [Fixed by microwave magnetron repair](https://microwaverepair.center/services/microwave-magnetron-repair/) 7. 07 moderate ### Browning works, microwave mode does not A speed or convection microwave has two heating systems. If the element browns but plain microwave cooking does nothing, the magnetron chain is the suspect; if the reverse, the element, its relay or the convection fan is. [Fixed by speed and convection microwave repair](https://microwaverepair.center/services/speed-and-convection-microwave-repair/) [On a built-in microwave](https://microwaverepair.center/types/built-in-microwave-repair/) 8. What it costs ### Every repair on the site's cost scale, side by side Open the cost guide ## What else it could be. Most often confused with loud hum, buzz or grinding from a microwave, then microwave shuts off before the timer ends. [All problems](https://microwaverepair.center/problems/) Codes that come with it - [`DEMO MODE` Bertazzoni · Mode, not a failure](https://microwaverepair.center/error-codes/bertazzoni-demo-mode/) - [`ERROR` Bertazzoni · Sensors and temperature](https://microwaverepair.center/error-codes/bertazzoni-error/) - [`DEMO ON` Bosch · Mode, not a failure](https://microwaverepair.center/error-codes/bosch-demo-on/) - [`SENSOR ERROR` Café · Sensors and temperature](https://microwaverepair.center/error-codes/cafe-sensor-error/) - [`FOOD` Café · Mode, not a failure](https://microwaverepair.center/error-codes/cafe-food/) - [`C-10` Dacor · Sensors and temperature](https://microwaverepair.center/error-codes/dacor-c-10/) [44 more codes, by make](https://microwaverepair.center/error-codes/) Also related - [**What a Microwave Error Code Is Telling You** 7 causes](https://microwaverepair.center/problems/microwave-error-code/) ### Loud Hum, Buzz or Grinding From a Microwave 6 causes ### Microwave Shuts Off Before the Timer Ends 6 causes Stop using it ### Sparks Flashing Inside a Microwave 6 causes ## The makes it happens on. 18 makes on this site; microwave runs but food stays cold can show up on any of them. Each mark opens that make's own page. [All 18 brands](https://microwaverepair.center/brands/) ## Microwave Runs but Food Stays Cold, where we come out. 9 metros, each with its own page. 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On a built-in, a drawer or a hood combination, usually yes, because the parts are a fraction of the unit and its installation. On an inexpensive countertop model a failed magnetron can make a new one the better buy, and we say so. ### Why does it heat on some days and not on others? A thermal cutout that opens when warm, a door switch near the end of its life, or a magnetron beginning to weaken all come and go. Note which days and what was cooking; the pattern narrows it down. ### Does a loud hum with no heat point to one part? Most often the diode, the capacitor or the magnetron. A heavy buzz with cold food is a reason to stop using it and book a visit rather than keep trying. ### What does demo mode look like on a microwave? On many models the display shows a demo word or a showroom icon, and the unit runs and counts down without heating. The manual gives the keypress that ends it, often a long press on one key. --- **[Read on the site: Microwave Runs but Food Stays Cold: Causes and Fixes](https://microwaverepair.center/problems/microwave-not-heating/)** **[Book a visit with MicrowaveRepair.center](https://microwaverepair.center/schedule/)**