# Microwave and Oven in Wall Combo. Micro dead. Help.



## homeimproverjoe (Nov 9, 2014)

I have a Bosch Microwave and Oven Combo. Model # HMC80251UC/01

About 6 months ago, the clock light started to dim significantly compared to the same clock light on the oven below it. The panel lights would only brighten up while the microwave was operating.

Last night, while microwaving a 3 minute dish, the microwave stopped dead, no lights, no sounds, nothing.

I opened the cabinet above the microwave and removed the shelf at the top of it and the area was pretty hot. The top of the micro was hot. I'm not sure if hotter than normal but we had also used the oven just earlier.

I turned off the breaker for about an hour to let everything cool down. When I switched the breaker back on, the unit was still dead. No beeps, chirps or lights.

Can someone tell me how to begin troubleshooting to find the problem and fix?


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## homeimproverjoe (Nov 9, 2014)

When opening the door, the light does not come on. Would that rule out the control board as fault?


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## BayouRunner (Feb 5, 2016)

Remove the exterior cabinet. Check your fuse first but since you said it was hot it most likely has a few limit switches. If any of those are open that would make the microwave not operate at all


Sent from my iPhone using Tapatalk


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## homeimproverjoe (Nov 9, 2014)

BayouRunner said:


> Remove the exterior cabinet. Check your fuse first but since you said it was hot it most likely has a few limit switches. If any of those are open that would make the microwave not operate at all
> 
> 
> Sent from my iPhone using Tapatalk


Thanks, any tips on how to check for that. Google search not too helpful on the topic.


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## BayouRunner (Feb 5, 2016)

Only just saw your response this morning. There is a limit switch on the magnetron, usually one on the cabinet as well. Check with no power and remove one lead, just make sure they ohm out or for better wording the circuit is closed. These limit switches look like a thermostat for a dryer but they are smaller. They are not resettable and once they trip they interrupt power to the microwave control board. They typically trip while cooking popcorn, sometimes you can physically see a bad connection (burnt wires or spades). Most of the times the wiring to the thermostat are black but that's most of the time, not all the time


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## BayouRunner (Feb 5, 2016)

You caught me at my desk this morning so I went ahead and looked it up. One limit switch is on top of magnetron, the other limit is towards the back above fan assembly for convection. Also unusual, microwave has two fuses so check both


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## homeimproverjoe (Nov 9, 2014)

I will take your advice and check the limit switches. I still need to locate them though. Not these right?


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## homeimproverjoe (Nov 9, 2014)

The only reference for microwave switches I can find are items 410 in the parts diagram below:










These are located just behind the door frame on the left and right top of the microwave. I can't see a switch of any kind on them. They just appear to be door switches.

Left Side:










Right Side:


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## homeimproverjoe (Nov 9, 2014)

BayouRunner said:


> You caught me at my desk this morning so I went ahead and looked it up. One limit switch is on top of magnetron, the other limit is towards the back above fan assembly for convection. Also unusual, microwave has two fuses so check both


If the switches are not in my pics above, can you share the link where you found them in diagram?


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## homeimproverjoe (Nov 9, 2014)

OK, more information. Very interesting!

So, I found that the first fuse (the fuse closest to the line input power) was blowing every time I turned the power breaker on. However, I bought a few more fuses to test and found that if I leave the door open prior to turning the power breaker on, the fuse would not blow and the microwave powers on. The clock light is lit like it should be.

And then when I closed the door, the panel immediately went dark and the fuse blew.

So, does that help identify the source of the problem? When the door is closed while power is on the fuse blows. When the door is left open, before powering on the unit the fuse does not blow and the microwave powers on fine.

So, when the door switches are open, the first ceramic fuse blows.

My suspicion is that item 410 needs to be replaced. However, there are two of them listed on the parts diagram, one on each side of the door. Can these be tested for continuity? Are they the likely culprit? They are $12 bucks each so If they are the likely cause, I'll just replace both of them.


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## BayouRunner (Feb 5, 2016)

The two green circles are what I call limit switches. Not the best terminology I guess but essentially when they get to hot they open as a safety switch. But from what your describing they are ok. I'm not sure of the problem your having but I will make a suggestion. Check the two or three door switches. Some manufacturers deliberately make the fuse blow if the door switch timing is incorrect. A good test for this would be to slightly lift the door while trying to close it with fuses in. If it works properly then your door is sagging and one of the door switches is not engaging or disengaging and is causing a short. On GE microwaves they use this design. I honestly don't know if bosche uses this system as well. 

Now with all that I could be way off base. You could try to see if magnetron is shorted by disconnecting the power wires. If unit runs without heating then that would be your issue, same thing for the transformer but they rarely go bad. Sorry I can't be of more help but I'm not familiar with the bosche setup. Also watch that capacitor. Some retain a charge and there is nothing nice about getting popped by one


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## homeimproverjoe (Nov 9, 2014)

I'm pretty certain I have a bad oven door switch. Its item 411 on the diagrams and there is only one of them. The switch is a normally closed switch. I tested for continuity with my multimeter on speaker tone mode. It beeps regardless if I press the green switch button in or not. The switch button does not click like the other two red microswitches do.

https://www.amazon.com/gp/product/B014RFR0PQ/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1


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## BayouRunner (Feb 5, 2016)

Very well could be


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## homeimproverjoe (Nov 9, 2014)

Here's some additional information for anyone who may have a similar issue:

The microwave is a combo unit that also does convection. There are 3 total door switches, two on the left side (microswitch and oven switch) and one on the right side (microswitch). The microswitches have red buttons and are normally open (NO) switches and the oven switch has a green button and is normally closed (NC).

The red switches, when pushed have a nice click sound. The green switch, when pushed does not click (perhaps this is normal). And I found that the green oven switch has continuity tone regardless if the green button is pressed or not.

So, in trying to determine what's happening with the switches when the door is closed, it appears that the microswitches, which are normally open, are then set to closed (continuity) and the oven switch, which is normally closed, is switched to open.

Why there is a single "oven" switch and 2 "microswitches" I'm not sure (I'd expect that they all would be microswitches unless the "oven" switch has a special purpose other than sensing when the door is open or closed). Also, why the microswitches are normally closed while the oven switch is normally open is another question I'm not certain of. Perhaps someone here knows?


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## homeimproverjoe (Nov 9, 2014)

I opened the suspect switch to confirm the issue (arced contacts stuck together). Here's what the failed switch looks like. The contacts should not be touching here. They appear to be fused together.


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## homeimproverjoe (Nov 9, 2014)

Solved. Changing out the door switch resolved the issue. The microwave operates as normal now.

I still have a dim control panel on the microwave when compared to the oven, however, that was happening prior to the switch failure and is not related. I think I have a faulty capacitor on the main logic board to blame for the dim panel.

Hope this thread helps someone. If your microwave won't come on, you may be able to determine if the door switches are at fault by doing the following troubleshooting step:

1) Turn power off at the breaker for the circuit your microwave is on
2) Insure your fuses are good - my Bosch combo microwave/oven in wall unit has two 20amp ceramic fuses.
3) Open the microwave door and leave it open for this test
4) Turn power on at the breaker
5) If the switch is at fault, your microwave should be powered on while the door is open, the interior light should be on and the panel should show as normal (clock, etc)
6) Now close the door. If the door switch is faulty, it should blow the fuse and the microwave will go dark.
7) Read above for how to troubleshoot a faulty door switch. Hint, if the little red switch button does not audibly "click" when depressed, the switch is faulty.


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## BayouRunner (Feb 5, 2016)

All the switches are designed as safety switches. One to keep you from being exposed to microwaves if door were opened and continued to run, also turntable will not function if switch is not in correct position, light turns on when you open door. Sounds like Bosche has a similar design to GE that deliberately shorts unit if switches aren't timed correctly.


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## homeimproverjoe (Nov 9, 2014)

I simply got lucky with the door open, power-on finding. Since the interior light should come on with the door open, I decided to open the door and leave it open while I turned the breaker on. To my surprise, the microwave had power again. The clock was lit and the interior light was on.

Once I shut the door, the microwave lost power immediately.

After shutting the breaker off, I then checked the fuse to find that it had blown. So, I surmised that closing the door had caused the fuse to blow. That led me to do some more searching and found that I needed to check the door switches for continuity. I found the bad one, replaced it, along with a new fuse, and voila, the microwave has life again.


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## mikecasarella (May 19, 2018)

Thanks so much for posting such detailed explanations. It seems I may be having a similar problem with my Bosch Speed Oven as well. It is also dead, but I can’t even reset the breaker for the circuit, it immediately trips. Did you have a similar issue or did the circuit breaker reset just fine but the internal fuses in the oven were blowing when the oven door was closed? Any thoughts on where to start troubleshooting if I can even get the circuit breaker to reset?


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## oberon148 (Nov 1, 2018)

Thanks Homeimproverjoe for your detailed post. I had the same problem with my Bosch microwave (same model). The problem was indeed one of the door switches (it was the "normally closed" one). Couldn't figure out why there was a dead short on one of the power lines. After reading your post, I checked the door switches, and one of them was fused closed. Got a replacement switch from local appliance parts place -- they're pretty standard, so don't need a "genuine Bosch part." I brought the whole switch holder with me to the store, to make sure that the new switch would fit. They sold me a switch that has both "normally closed" and "normally open" connectors. Make sure you use the right connectors when reconnecting! One other note is that the internal ceramic line fuses are *inside* the microwave, on a board that's located near the top of the oven, at the upper right back corner of the oven. The fuses are 240V 20A.


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## Domo (Nov 9, 2018)

A a


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## Rangeguy (Apr 3, 2020)

2020 Update. I had the same problems generally as those described above and found this site when looking for help. The problem is now fixed but many mistakes were made along the way, this posting is as much a parody as it is (I hope)helpful.
*Mistake 1*, I read this stuff about door switches and more switches and thought this is crazy, found the blown fuse replace everything fine. Boy, aren't i the wizard. Three days later BOOM! In retrospect, i can't explain why it functioned for three more days.
So i backup and start looking for these door switches, two or three, right side left side.
*Mistake 2* The two swithces on the left side are held by the same holder, one NO and one NC switch, thank you to homeimprovementjoe, GREEN is NC and RED is NO. The NC switch GREEN was fried. Here's my mistake when i was looking for the switches i looked right past the switch on the right side and concluded there was none. In fairness, there is no evidence of a switch when viewed externally from the outside, unlike the left side.
Received the GREEN NC switch and installed, fuse blown. WHAT? Revisited the search mode and sure enough, the RED NO switch on the right side was revealed and blown.
A couple of thoughts, once you identify and understand these microswitches they are relatively easy to purchase (online). Yes the switch holders seem to be constructed so as to not allow the switches to be replaced (they break), some order new holders and i decided that i damn sure never be required to replace these switches again so a spot of superglue secured them. I would also suggest that replacing all three switches is a good idea. Did i mention that i replaced the front control panel four months ago? Not real happy with my Bosch combo.


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## jceballos8 (May 4, 2020)

So does anyone have links to the switches and fuses that need to be replaced. Im going through the same issues with my Bosch. First the display went really dim then one day it stopped working all together. I just bought a new control panel thinking it had to do with the dim display. Once I replaced the control panel, the microwave still did not turn on. I have a voltage tester and I am getting power to the microwave it just wont turn on. So fustrating, very disappointed with this expensive appliance. So Ill try the switches to see if they work, but if anyone has link to the switches and fuses please let me know. thanks!


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## larryca2 (May 11, 2020)

Wall mounted Bosch microwave keeps blowing the left fuse, even with the door open. Could this be the control panel? I looked at the control panel and thought it was a leaky capacity problem, so I replaced the cap. That didn't fix the issue but did note that the PC board had a burnt spot very near the previously suspect blown cap. 
Would a bad controller board cause the fuse to blow?


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## jceballos8 (May 4, 2020)

Rangeguy said:


> 2020 Update. I had the same problems generally as those described above and found this site when looking for help. The problem is now fixed but many mistakes were made along the way, this posting is as much a parody as it is (I hope)helpful.
> *Mistake 1*, I read this stuff about door switches and more switches and thought this is crazy, found the blown fuse replace everything fine. Boy, aren't i the wizard. Three days later BOOM! In retrospect, i can't explain why it functioned for three more days.
> So i backup and start looking for these door switches, two or three, right side left side.
> *Mistake 2* The two swithces on the left side are held by the same holder, one NO and one NC switch, thank you to homeimprovementjoe, GREEN is NC and RED is NO. The NC switch GREEN was fried. Here's my mistake when i was looking for the switches i looked right past the switch on the right side and concluded there was none. In fairness, there is no evidence of a switch when viewed externally from the outside, unlike the left side.
> ...


I’m going to tell you right it’s the door switches. I had the same problem with the fuses. You have two micro switches on the left side and one on the right side. My right side switch went bad. I ordered the replacement from the
Bosch site since the price was just a few dollars difference. I ordered all three fuses. Many have said the support for the switches broke when removing the old switches but I was able to remove them without a problem. But you can’t manage not to break them, just order those too. 
I’m going to tell you right it’s the door switches. I had the same problem with the fuses. You have two micro switches on the left side and one on the right side. My right side switch went bad. I ordered the replacement from the
Bosch site since the price was just a few dollars difference. I ordered all three fuses. Many have said the support for the switches broke when removing the old switches but I was able to remove them without a problem. But you can’t manage not to break them, just order those too.


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## RobStl (12 mo ago)

I've had the same problem but still can't resolve it. Microwave stopped working including display not lit. Long story short, I replaced all three door switches and the blown fuse. As soon as I close the door, the microwave goes dead again. Based on the above, a faulty switch is blowing a fuse, but the fuse is still blowing when the door is closed even with three brand new switches. I know the microwave still works because at first I just replaced one switch and a fuse. I ran the microwave one time. Opened the door then closed it, then it went dead. I replaced the other two switches, left the door open, turned on the breaker, microwave was lit up, then closed the door and microwave went dead.

Any suggestions?


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## huesmann (Aug 18, 2011)

Sounds more like a short than a faulty switch, if it keeps blowing.


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