My Galaxy 721.80002401 microwave just quit heating and rotating. Everything else, including the exhaust fan works fine.

check the air filter and cooling fan.

Yes, there is a thermostat device located on the magnetron. It will open up (turning off the magnetron) when it gets too hot, and it will reset automatically after it cools back down (in 5 to 15 minutes). The question is, Why is is over-heating? Usually it is caused by the exhaust fan being turned the wrong way. (For example, it may be set to exhaust the air out through the top of the microwave, but you don't have a vent there.) That fan can be turned to exhaust air out the top, out the back, or recirculate the air back through the front of microwave. It's easy to turn it around - the hard part is that you have to take the microwave down to be able to pull the fan out and rotate it the right direction.

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The motor for the rotator is bad. It has to be replaced.

whirlpool microwave keep working when door open why

Could be the magnatron/thermal cut out seek pro advice

Hi,
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heatman101

hfkk

The Magnotron goes out on many of the lower priced models in the first yr.,(and some of the higher end ones too!) As the components there do most of the hard work. Better to just find a recycler who takes them and scrap it.
As for the replacement that sounds like an excellent idea!

Oh, it turns out the the microwave was over heated and the fan was cooling it. The fan will automatically turn on and stay on until your microwave reaches normal temp. just unplug your microwave and let it cool off. then plug it in and everything should be just fine.

Hi , open the cover with philips screw driver , b sure unplug it first , If you have continuety tester check the fuse if open replace it , are available in electronics center brings that sample and insert it.

Does the turntable rotate? If everything but this works (except no heat), you probably have a bad door switch. Here's a discussion of what's involved in replacing it: http://www.fixya.com/support/t267796-kenmore_microwave_hood_combination_over

If the turntable does rotate, I'd suspect a more significant failure, such as the transformer, capacitor, or magnetron. If it's any of these, it's time to replace the unit.