[Walt Lamb]

Problem: Won't heat - all other elements work. Problem caused by using microwave without anything in the oven. Tried to use as timer but failed to cut on timer mode . After a few minutes fan cut on. After that no heat.
My guess is magnetron but would like to see if there may be a fuse. All lights and turntable motor works ok. My warranty says that there is a 5 year against manufacturer workmanship or materials. I don't think I fall into that catagory.

[Gene]

There are no such fuses in your microwave. Very likely the problem is a bad magnetron and if the microwave is less than 5 years old then it should be under the limited warranty (part only).

Here are the break down diagrams and Replacement parts for MAYTAG MMV4205AAW | AppliancePartsPros.com

Gene.