Thread Number: 71875  /  Tag: Small Appliances
Microwave oven starting by itself
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Post# 950791   7/30/2017 at 13:30 by fan-of-fans (Florida)        

This weekend I went to put something in the microwave and when I closed the door, it turned on by itself. I didn't press the buttons or anything, it just started up. There were no minutes showing on the display, just the clock. I tried pushing stop or setting the timer but the buttons didn't respond other than making the beep noises. I had to open the door to make it stop, and when I closed the door again, it started up again on its own. Finally the second time I tried it, it functioned normally and hasn't done it again. But I was told several weeks ago at least, maybe a month ago that it had done this same thing.

It's a Kenmore microwave, not sure who made it and it's about 15 years old. Otherwise it works fine. Although once in a while when the time is up, it doesn't do the beep beep beeeep to let you know it's done, it just stops running with no beep.

Post# 950807 , Reply# 1   7/30/2017 at 16:39 by Frigilux (The Minnesota Prairie)        

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Post# 950823 , Reply# 2   7/30/2017 at 19:05 by panthera (Rocky Mountains)        
Our GE Spacemaker II

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Does that every so often - although the magnetron isn't on, just the fan. I figure it's just a poor quality logic board.

Post# 950828 , Reply# 3   7/30/2017 at 19:47 by GusHerb (Chicago/NWI)        

Our 14 year old GE convection oven does this periodically as well, the magnetron doesn't engage in this case either, so I never thought too much of it.

Post# 950845 , Reply# 4   7/30/2017 at 22:55 by sudsmaster (East of SF, West of Eden)        

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Offhand I'd say is unplug that thing and either take it to a repair shop or toss it in the trash.

Post# 952751 , Reply# 5   8/13/2017 at 13:36 by e2l-arry (LAKEWOOD COLORADO)        
Mine did that too!

It was a JC Penney or whoever made it for them. Bought in about 1982. One day in 1996 I came home from work and it was running and VERY hot.Even the dishes in the cabinet above it were warm. I unplugged it and would only plug it in when needed. But I'd occasionally forget to unplug it again after. Then, the second time I came home and found it running, and again VERY hot, I retired it before it started a fire or something.

Post# 952760 , Reply# 6   8/13/2017 at 14:08 by DADoES (TX, U.S. of A.)        

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Haven't yet had a microwave oven exhibit such behavior in all the specimens since and including the 1979 Whirlpool.

Post# 952764 , Reply# 7   8/13/2017 at 14:23 by realvanman (Southern California)        
Sticky relay?

Or faulty control board?

I can't see any other possibility.

Post# 952795 , Reply# 8   8/13/2017 at 18:54 by sudsmaster (East of SF, West of Eden)        

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The reason why I suggested junking it is because microwaves can be quite harmful to people. If this thing is starting on its own, who is to say it might try to start when you have its door open? That could cause severe injuries.

In addition to the fire danger.

Post# 952797 , Reply# 9   8/13/2017 at 19:53 by iej (Ireland)        

You sure it's not just a cooling fan?

Post# 952802 , Reply# 10   8/13/2017 at 20:43 by combo52 (Beltsville,Md)        

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No MWO has ever operated the Magnetron with the door open, the way the door switches are designed it is just not possible.


In addition No One has ever been injured by  microwave energy from a home MWO. They are one of the safest electrical appliances ever made.


I have seen many MWOs that have had the cooling fans run with the door open, and I have seen a few that have actually started when not called for with the door closed. If you have one that actually starts cooking without you starting it you should have it repaired or replace the MWO.


John L.

Post# 952823 , Reply# 11   8/14/2017 at 00:52 by tolivac (greenville nc)        

Microwave ovens are equipped with a fail safe "monitor" circuit to disable the oven if it should ever try to start the magnetron with the door open.A fuse inside the oven will blow-disabling it and alerting you that the machine is defective.The oven has to be taken apart to replace the fuse-and you will need to replace the bad door switches.At that point--just get a new machine.Agree with John-you are more likely to get hurt by a microwave cooker by having it fall on your foot!I dealt with the monitor switch once-told the owner to get a new machine.Was on a very old Radarange or whatever those were.

Post# 952827 , Reply# 12   8/14/2017 at 01:40 by DaveAMKrayoGuy (Oak Park, MI)        

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Keep a Pyrex measuring cup of water in that thing...

-- Dave

Post# 952861 , Reply# 13   8/14/2017 at 09:55 by cadman (Cedar Falls, IA)        

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FYI, the 'chrome door' Radaranges have a very elegant monitor switch circuit that has always impressed me. Rather than the 'brute force' dead-short approach taken by other manufacturers (that requires switch replacement), in the RR, a wire wound resistor is placed in the circuit and a thermal cutout is run through it. The resistor heats up and opens the cutout within seconds but also limits current through the switch contacts. Being these machines were designed to be repaired, it makes sense Amana/Raytheon engineers would go to that level of trouble.

Today the only time I see a monitor switch failure on these is when a door spring breaks. For many of these RR's, it's the first time the cabinet seal has ever been broken.

Post# 952899 , Reply# 14   8/14/2017 at 15:46 by cuffs054 (GA)        

I'd call a priest.

Post# 952903 , Reply# 15   8/14/2017 at 16:00 by kenwashesmonday (Haledon, NJ)        

combo52 wrote:
"No MWO has ever operated the Magnetron with the door open, the way the door switches are designed it is just not possible."

I've personally seen it happen. There was a cheap microwave in the kitchen in the pizza shop where I worked around 1980 which was only used it for defrosting Italian bread when we ran out. Yes, the darn thing would run with the door open. We pointed it out to the boss, he threw it in the dumpster, and we did without a microwave from then on. I don't remember what brand it was, this was over 35 years ago.

Post# 952926 , Reply# 16   8/14/2017 at 20:05 by fan-of-fans (Florida)        

I don't believe the magnetron was actually on when this happened, just the fan. I felt the food inside and it didn't feel at all warm.

I remember my aunt had a Frigidaire over/under electric range at her beach house (it may still be there now, but not sure) and it had the microwave on top. I seem to recall there was a button that could be pressed to turn on a fan in the microwave, and then the timer could be set and start button pressed on the keypad if the door was shut. But my grandmother pushed the button that started the fan while she had the door open and my aunt got a bit startled that the microwave was actually running with the door open. However, it was just the fan.

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