So, this is a big combo wall unit (microwave & convection oven). It first stopped heating about 2 years ago. Replaced the diode and magnetron myself with non-OEM stuff, worked fine for another year.

6 months ago, it stopped heating again. No other warning signs, no error messages, oven works fine; everything is totally normal, except the microwave does not heat.

Bought an OEM magnetron and put it in - everything was great for two weeks, then it stopped heating.

Put in another off-brand magnetron - again, worked great for two weeks, then stopped heating. Again, everything else looks and appears normal.

Had an applicance guy come out and tell me to try replacing the thermostat and capacitor this time around. Did that, and once again, the microwave worked and heated fine for about a week.

This morning, once again, it stopped heating. I turned off the breaker to the whole unit to see if cutting its power for a couple of hours would help, but it did not.

SO, dear experts - what would cause the microwave to work just fine for two weeks every time I take it out and replace something, only so suddenly stop heating again? If it were some kind of fuse issue, it would never heat until I replaced that, but I haven't replaced any fuses. There appears to be some part in there that, after having pulled everything out, "resets" itself and works fine for a short while, and then craps out and causes the dreaded no-heat scenario.

Anyone have any idea what component could be the culprit here? Have a Whirlpool-certified technician coming out next week to try to solve the mystery, but if anyone can beat him to the answer, I would be super appreciative.

Thanks for any help!

Follow-Up #2:

I received the new door switches and (for like the 20th time), removed the microwave from the wall and set it on the table to work on it. Got it apart and quickly discovered there are THREE, not two, door switches, though I had only bought two. Anyway, long story short, there's a great appliance parts store near my house, so I went there and got one more.

I put the new switches in - indeed, it was a frighteningly easy swap out - and reinstalled the microwave and turned the power back on. And.... success! Things are working great right now. Of course, it hasn't been a week yet, and I've only gotten a week or two out of previous fixes, so we'll see if this one holds. I will say this, though - the swapped out switches looked BAD - brown, burned-out looking contacts, all three of them on all three switches, so I HAVE to believe that was the culprit after I had tried just about everything else.

Anyway, I'll be back in a month or two to share any updates for those that are curious.