Yesterday microwave worked fine today it doesnt heat anything and power level does not show up on the led screen kenmore model 721

Chances are that is just a defective top or bottom door switch or its mount.
See our help file on door switches here.
Also, that model number does not show up as a valid US Kenmore model.
Please check the tag in the cooking cavity or elsewhere n the oven and let us know if you need further help.

Hi,
On the link below is the list of Kenmore microwave oven model manuals starting with 721.Click on selection to download.

www.managemylife.com/mmh/owner_manuals/search?query=Kenmore+micicrowave%2Fhood+combo+-+7218924680

Hope this helps.Thanks!

Hi,
Here is a tip that will help you to figure out what is wrong with yourMicrowave Oven....

Microwave Oven Basic Troubleshooting Tips

heatman101
fgghf

In all likelihood the mangnetron has failed, or perhaps even the Power Supply. or a fault that is shutting the system down for safety reasons You need to have it serviced by a reputable service centre/man.
Ensure you get a firm "Quote" before proceeding, and remember these days the cost of repair can equal or exceed the price of a new one.

The service manual is here.

Unless there's a bad connection at a magnetron terminal, I would say you have a failing magnetron.

It is part number 2B71165R and you can get it from the Pros here for $68.59 (subject to change).

For more free DIY and other help & advice, feel free to contact me via my site.

William E. Miller, AS-EET
http://www.microwavecontrol.com
Microwave Oven Control Panel Repair Nationwide
"Recycling by repairing since 1982"

Try first unplugging power cable for ten minutes, and see if it clears the error.

This is most likely a failing magnetron.

If it's less than 5 years old, Sears/Kenmore should cover the part, but you would still have to pay for a service call.

If you or someone you know decide to work on it, we have *critical* safety, disassembly, and troubleshooting info at our site, and our link is at our listing here on FixYa: http://tinyurl.com/yzjozk

We're happy to help and we appreciate your thoughtful rating of our answer.

The "HUMM" indicates a breakdown in the High Voltage Side. The loud "POP" was the breakdown. You have only four Components in the High Voltage side.

1. High Voltage Transformer. You can eliminate this as the problem. Why? If it was the problem it would have blown the line fuse, and would have given off a burned transformer smell.
2. High Voltage Diode. Usually will Burn or Pop when shorted, but will then OPEN the Circuit and there is no "HUMM".
3. High Voltage Capacitor.This is the Silver Can with the two terminals on top. It can SHORT internaly between the plates (the two terminals) and give the "HUMM".
4. Magnetron. This is my number one suspect. A SHORTED Magnetron.

Disclaimer: I'm a DIYer, not a technician.

Our GE over-the-range microwave stopped producing heat yesterday while warming part of the T-giving feast. Everything else (fan, control panel, light) works fine.

After disassembly and testing last night, I discovered a defective "secondary door switch." Your Kenmore uses a similar switch (~$19 on-line), and that might be the problem. But it also could be other things, such as a bad thermal cut-out.

If you know anyone who's handy with a multimeter, most of the basic diagnostics seem to be pretty straightforward.

It is child lock and you can unlock it by press and hold the start button.