20 Most Recent Kenmore Elite Microwave, Model 721.66339011, Open Box tbc827 Questions & Answers

Replace bad kichen timer. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0CGEQFjAIahUKEwjzg_qe1qTIAhVHGh4KHV_QA0k&url=http%3A%2F%2Fwww.polder.com%2F_literature_108997%2F890-90_Single_Kitchen_Timer&usg=AFQjCNFR_4SdFyRmHQ9HCRxaVR5vIX4Mqw&sig2=KCGeIyimjx5FE21sb-zZPw&cad=rja

hi , now that's either power supply to power the magnetron or the magnetron itself ... Regards Rob

in a microwave

You probably have either a shorted high-voltage capacitor, or a shorted high-voltage transformer. And there is a 3rd possibility that should be checked first - the so-called "monitor switch" may be stuck in the closed position. There are usually 3 door switches in most microwave ovens, although some have 4. The monitor switch is usually the the one located in the middle of the door latch area. If you need further help, reach me via phone at https://www.6ya.com/expert/ronald_e6b9572cebe3ad27

Frequently this is caused by a loose connector to a thermal protection device (a TCO) or some other connector that has a plastic sleeve over it. The connector is loose, which is causing heat, which is melting the plastic. You would have to remove the cover to find the bad device and connector. This is a job for a professional microwave repairman. If you need further help, reach me via phone at https://www.6ya.com/expert/ronald_e6b9572cebe3ad27

Open box, huh? It may be possible that you don't have the right tray for that microwave. If you need further help, reach me via phone at https://www.6ya.com/expert/ronald_e6b9572cebe3ad27

Apply a LITTLE BIT of grease to the door latches. If you need further help, reach me via phone at https://www.6ya.com/expert/ronald_e6b9572cebe3ad27

If this isn't close to what you have, search on youotube - there are lots of microwave door switch videos!

No power at all would point to a breaker or fuse for the power. You would have to open the back to have a look and test for voltage.

Microwave Error Code F9 Troubleshooting

This is a 2.0 cu ft model. link to user manual: http://kitchen.manualsonline.com/manuals/mfg/kenmore/721_7920.html?p=1

Call Sears and complain. Visit the Consumer product Safety Commission website. Between the two you should get all the info you need.

Most likely it would be a bad magnetron since the light, turntable, and vent fan are running.

It turns itself on

1. Interlock switch If your microwave is turning itself on, the first thing to check is the interlock switch. This is usually the first thing to malfunction that could cause this issue. If the interlock switch is bad then it will need to be replaced.
2. Main control board If your microwave is turning itself on and the interlock switch is still working, the probable cause is the main control board. If the control board is defective it will need to be replaced.

But before throwing parts at it give these folks a call... https://www.repairclinic.com/RepairHelp/How-To-Fix-A-Microwave/74-6-878350-/New/Kenmore-Microwave-Turns-On-By-Itself-721-85033010 Best to you