If a microwave appears to cook or continue operating with its door open, stop using it immediately. Do not run another cooking cycle to find out whether it is heating. The FDA advises discontinuing use because a consumer cannot reliably determine whether microwave energy is being emitted in that condition.
A cavity light turning on when you open the door is different from unexpected cooking operation. Some models also have separately controlled ventilation or cooling fans. Check the exact owner’s manual, but do not treat a running fan, moving tray, or familiar sound as proof that a suspected door-safety fault is harmless.
Normal light or a stop-use warning?
| What you already observed | What to do next |
|---|---|
| Only the interior light comes on when the door opens; there is no unexpected operating behavior. | Compare this with the lighting description in the model manual. |
| An over-the-range ventilation fan continues after cooking. | Check the manual’s cooling or ventilation explanation. If the behavior is unclear, contact the manufacturer without running a test. |
| The appliance unexpectedly starts, the tray runs with the door open, or cooking appears to continue. | Stop using it, isolate power safely, and arrange qualified service. |
| The door, hinge, latch, or sealing surface is damaged, or the door does not close firmly. | Do not operate it, even if it still heats food. |
What to do immediately
- Stop the cycle. Use Stop/Cancel if it is safe to reach. Do not open and close the door repeatedly to reproduce the fault.
- Disconnect power safely. Unplug an accessible, undamaged plug with dry hands. If it is built in or the plug is inaccessible, use the correctly identified circuit breaker if safe. Do not pull a heavy appliance out, reach into damaged wiring, or unmount an over-the-range unit.
- Keep it out of use. Tell other household members not to reconnect or operate it while service is pending.
- Record what happened from memory. Note which light, fan, tray, or display was active and whether a cooking cycle had been selected. Do not recreate the event for a video.
- Contact the manufacturer or an authorized microwave service provider. Supply the full model and serial number from an accessible label, plus the symptom description.
If there is smoke, fire, sparking, or a damaged electrical connection, move away and seek emergency assistance as appropriate. Do not attempt internal repairs.
Do not use an open-door water test
Never wedge the door open, hold a latch in, bypass a switch, or heat a cup of water with the door partly closed to check for microwave energy. Whether the water feels warm is not a safe diagnostic method. Do not use a phone, a household radio, or improvised equipment as a leakage detector.
A reset that changes the symptom does not demonstrate that the door-safety system is working correctly. Leave the appliance disconnected until the manufacturer or qualified technician has evaluated the reported fault. A normal no-heat test belongs only to an undamaged appliance without a suspected door-safety problem.
Why this is a service job
Microwaves use interlock systems intended to prevent microwave generation when the door is open. Unexpected operation may involve the door mechanism, an interlock, wiring, or controls; the symptom alone does not identify a failed part. There is no defensible universal percentage that proves a door switch is the cause.
Do not remove the cover, replace a door switch, adjust latch alignment, or touch internal wiring. The CPSC warns that microwave repair can expose hazardous voltage even after the oven has been unplugged. Unplugging it protects against ordinary operation; it does not make internal components safe to handle.
Information to prepare for the service visit
- Brand, complete model number, serial number, and approximate purchase date.
- Countertop, built-in, combination-oven, or over-the-range installation.
- Whether only the light came on, or a fan, turntable, timer, or cooking function also behaved unexpectedly.
- Any visible door damage, loose hinge, unusual latch behavior, error message, smell, or breaker trip.
- Whether the event followed cleaning, a spill, impact, installation, or repair.
- Any warranty or recall information supplied by the manufacturer.
Ask the service provider to explain the diagnosis and the model-specific safety checks needed before returning the oven to use. If replacement is recommended, have a qualified installer handle removal and installation of a built-in or over-the-range unit.
If the problem is no heat instead
If the door operates normally and there is no suspected door-safety fault, our LG no-heat guide and Samsung no-heat guide cover external checks for those brands. Do not apply their cooking tests to an appliance that appears to operate with its door open.
Sources and scope
- FDA: Microwave ovens, door safety, and when to discontinue use
- CPSC: Electrocution hazard with do-it-yourself microwave repairs
Substantially revised September 27, 2026. We removed an open-door heating experiment, reset routines presented as repairs, unsupported diagnosis percentages, and instructions to replace internal door switches. This is a documentation-based safety guide, not a hands-on test or a diagnosis of your appliance.
