Why does my microwave run but not heat food?

A microwave that runs but does not heat usually has a failed part in the circuit that makes the microwaves, and that repair is for a technician. Start with two free checks, then decide whether the oven is worth fixing.

What "runs but does not heat" means

When you press start, the light, turntable and fan can all work because they run on separate, low-power parts of the oven. A device called a magnetron inside the oven produces microwaves.^[3] The heat comes from those microwaves, not from the light, fan or turntable. If the magnetron or anything that feeds it stops working, the oven keeps spinning and humming along while the food stays cold. GE puts it this way: there could be one of many components that is not working properly.^[1]

That is why the symptom alone cannot tell you the cause. Several different failures look identical from the outside, and telling them apart takes a meter.

Two checks that cost nothing

Both checks happen outside the case, so they are safe to do.

Check the settings. Make sure the "Timer" function was not inadvertently used, which is the first tip GE lists.^[1] A reduced power level can also make food come out barely warm, so confirm the oven is on full power.

Close the door firmly. GE says to open the door and close it firmly, which confirms the engagement of the door's safety mechanisms.^[1] FDA says the standard requires two independent interlock systems that stop the production of microwaves the moment the latch is released or the door is opened, and that a monitoring system stops oven operation in case one or both of the interlock systems fail.^[3] A latch that is not fully engaged, or a worn door switch, can therefore stop the heating while the rest of the oven seems normal.

Check what you are heating

Before blaming the oven, try a cup of water. FDA says microwaves are absorbed by foods and cause the water molecules in food to vibrate,^[3] and that foods that are high in water content, like fresh vegetables, can be cooked more quickly than other foods.^[3] Dry food, or food in a container the waves cannot reach, will come out disappointing in a perfectly healthy oven. FDA also says generally, metal pans or aluminum foil should also not be used in a microwave oven, as the microwaves are reflected off these materials causing the food to cook unevenly and possibly damaging the oven.^[3]

If a cup of water is still barely warm after a normal heating run, the oven has a real fault. Some ovens should not be operated when empty,^[3] so keep the cup of water in the oven and check your manual.

Why you should not open it

Do not take the case off, even with the plug pulled. GE says it offers "no do-it-yourself repair advice on microwave ovens" for safety reasons, citing a capacitor that can hold a high voltage charge even after it has been unplugged, complex electronic circuitry, and special equipment needed to make a diagnosis.^[2] Its words: "We urge you NOT to attempt any microwave repairs."^[2]

The risk is not only a shock. FDA says there have been very rare instances of radiation injury due to unusual circumstances or improper servicing.^[3] What a technician does with a meter, and in what order, is covered in what a technician does to fix a microwave that will not heat.

Stop using it if

• The door does not close firmly, or is bent, warped or otherwise damaged. FDA recommends not using an oven if the door doesn’t close firmly or is bent, warped, or otherwise damaged.^[3]
• The oven keeps running with the door open. If an oven continues to operate with the door open, FDA recommends immediately discontinuing use of the oven.^[3]
• You see sparks, smell burning, or the oven trips the breaker.

If the door hinges, latches or seals are damaged, FDA says to contact the manufacturer for assistance.^[3]

When to call a licensed pro

If the door and settings are fine and a cup of water still does not warm, GE says: "we recommend contacting service."^[1] Call a qualified appliance repair technician, and for a built-in or over-the-range unit ask who handles taking it out of the wall or cabinet.

Ask each business for its visit fee, whether that fee is credited toward the repair, which part it believes failed, and what is covered if the new part does not fix the problem. Ask for the estimate in writing. DPOR's hiring guide says it is advisable to get at least three written bids or estimates using identical plans and specifications so you can compare prices.^[4] The same guide says: Do not automatically accept the lowest.^[4] A quote that is cheap because it skips the diagnosis is not a bargain.

Whether the repair makes sense depends on the oven's age and price, which is the subject of whether it is worth repairing a microwave.

Getting help in Virginia

Browse more appliance repair answers, see appliance installation businesses for a built-in unit that has to come out, or look at microwave repair businesses.

When you are ready, describe the microwave problem once and local appliance repair businesses quote it.