Fan runs when door is closed - no heat

SOMETIMES A DOOR SWITCH GOES BAD AND BACK FEEDS POWER THAT RUNS THE FAN AND IF IT HAS IT SOMETIMES THE TURNTABLE TOO SO YOU HEAR THE FAN RUN ALL THE TIME BUT TYPICALLY IT IS NOT HEATING. YOU COULD PUT A SMALL CUP OF WATER INSIDE TO SEE IF IT IS HEATING, PROBABLY BAD DOOR SWITCHES OR BAD CONTROLLER.

THere are three possibilities, open magnetron "heats food" cracked high voltage diode, or a shorted high voltage capacitor.

Our microwave in office won't shut off. It continues to heat and fan is running as soon as we close the door. Tried everything, unplugged, canceled everything. Please let me know what to do.

With the model number, we can offer more specific advice or an estimate.

But since FixYa does not notify us of follow-ups, you will need to post a new help request.

If the oven is doing everything else properly (light comes on, fan runs, turntable goes around) but there's no heat, you may have a failed magnetron tube (the microwave source). There's also a relay that controls power to the tube that may not be working correctly, or the control circuit board is bad. It's also possible one of the door switches is not working (so the oven thinks the door isn't closed), although this usually keeps the turntable and fan from running.

Microwave oven service is not for do-it-yourselfers. There are potentially deadly voltages present even with power off, and a chance of microwave leakage if repairs aren't done properly. Let a professional give an estimate to repair it, or just replace it if it's under $100. (When I was servicing these things it wasn't unusual for a repair to cost over half the price of a new one. That's one of the reasons so few shops still work on small appliances.)

Hi firstly to see if it is producing energy, buy some 5mm light emitting diodes from an electronics store. cut off the leads close to the plastic body.
place in microwave and put on cook for max 10 secs, if the led's light up you have microwave energy, shut off the oven as soon as they glow otherwise you end up with a mess.
If you have energy then your problem is most probably the door interlock micro switches which after time do not operate properly. let me know the results and we can go further.

Sounds like a door switch problem or stuck relay contacts on the control PCB. Do the light and fan run too or just the T/T??

It's probably a bad door switch or switch mount. If you or a friend decide to work on it, we have *critical* safety, disassembly, and troubleshooting info (as well as a text file which helps in diagnosing and repairing door switch problems) at our site, which is linked at our listing here on FixYa: http://tinyurl.com/yzjozk Feel free to contact me directly if you have further questions. I appreciate your thoughtful rating of my reply.