Repair and disassembly guides for microwave ovens.

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Microwave seems to come on, but only heats occasionally?

I have a Kitchenaid Microwave KEMS378GSS0. So the lights on, the fan's running, and the carousel is turning, but only intermittent heating. Before you jump in with the magnetron needs replacing, please read on. The thing is, I've found pushing on the door handle or a light 'thump', is usually enough to start the microwave heating when it's not (or stop it sometimes, if it was heating.) There's a noticeable 'thrum' (noise of some electrical part engaging) when that happens, even after the microwave has already started. I figure it's either a bad sensor or a mechanical issue like a loose connection or bad switch... but I was hoping to narrow it down before pulling out and apart our 8 year old built-in combination microwave & oven.

I do have some (slight) experience with repair work and circuits, but the expanded parts diagram really doesn't help show how everything is connected. At the moment the best I can come up with is one of the three microswitches that are part of the latching assembly serves as an additional safety keeping the magnetron from engaging and it's going bad?? That's where I'm stuck. It's the best I can guess at, but it doesn't make sense to me why the microwave would come on at all instead of just reporting a door open error if one of the switches was intermittently working.

So I'm here looking for experience with microwaves... Someone familiar with their design and/or repair who might make other suggestions as to what to look for when I do try and fix this beast. Or maybe someone that can confirm if it makes sense that one of the latch microswitches going bad (sticking, whatever) could in fact allow the microwave to come on but not heat up.

Thanks for reading,


Answered! View the answer I have this problem too

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Does no one have a clue what the problem might be, or did I do something wrong with this post?


What's the model number?


Kitchenaid KEMS378GSS0


One last addition. SHould I consider replacing anything else while I have the built-in out and partially taken apart anyway?

The fans and blowers are all still working, but was just thinking it might make sense to plan on replacing some of the mechanical parts with the most wear while I had the unit out anyway.

Any thoughts?


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2 Answers

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For anyone interested, I did finally fix this. Replaced 3 door switches to no avail. Further checking while it was apart revealed that the door wasn't closing 100%, so one of the door switches (interlock #2) wasn't engaging. Top part of door looked spread slightly, which seemed to be what was keeping it from working. Maybe a result of taking the door apart repeatedly to replace the torsion springs. I finally just dremeled the inner edge of the two latches on the door so that the rotating mechanisms that the microswitches sit in could turn an extra mm further. (a little counter-intuitive because the latches first turn the disks inward, but when mostly in the springs push the disks in the other direction so that the latches are then keeping the disks from turning further.) That pretty much did the trick. Not perfect, but the switches do engage 95% of the time when closed. If not and the light's on, a light push or tap is enough for it to register as closed.

PS. As I was trying to fix this, the MW changed to beeping error that the door was open, where before it would actually turn on but magnetron wouldn't engage. With a little searching I found the Buss fuse had also likely failed, probably as a result of my tinkering. Another trip to hardware store for a $3.50 part and it's back to working!

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I seen the same thing on mine and I put a band-aid on the door and that kept it out enough to make the switch. I like to get mine fixed because it was a gift from my mom who since passed. It is doing the same thing as yours, heating sometimes and not others.


Larry G, if you have any questions, just let me know. BTW, the problem started up again. The microswitch on the left side of the MW door just wasn't engaging all the time. This time when I took the MW apart I realized there was a 2nd spot where the microswitch could be installed that made it contact a hair sooner than the original position. Moving the switch there has made it work 100% for me once more. Good luck.


Mine was doing the same, I'm not sure what the culprits was. I'd taken mine apart everything tested fine I plugged it up and it worked. It's humming along fine rite now.


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Most of us won't work on these because they can kill you. The consensus seems to be to chunk it and get a new one.

FYI - Here's how to discharge one:

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I understand. It's just a little pricy to replace when we're talking about a built-in micro-range combo compared to a stand alone micro.

I was just hoping someone could confirm that something like a bad microswitch in the latch might ONLY stop the magnetron from turning on, but everything else runs as if fine. Or if not, what else might be affected by just pushing on the door.


I'd go here and start replacing door latch parts:


Thanks, but from my personal experience with this model, I'm pretty sure that's the oven door latch.

The MW assembly and the three latch micro-switches (part 73 - 4375346) I was looking at foremost , is here:

If I don't hear any other opinions, I'll probably go ahead and order a couple of those switches and plan on switching them out (if I can find the one that's has flaky continuity, or just the ones the look the worst.)


In the dotted box on my link, I think you'll find those switches.


If it is, I'm missing it. The parts 12 and 13 in the oven latch are not the same part #s or prices as the three switches in the microwave latches in the 'cabinet and stirrer' diagram.

12 - 4452312

13 - 4456568

73 - 4375346


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Dan M will be eternally grateful.
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