As I understand your question, everything works in your microwave except there is no heat, is this correct?
Typically there are two common reasons for no heat. The third is very expensive. I will cover the problems in order.
1) Do you regularly open the oven door while the machine is running? If yes, every time you open the door, the door safety interlock switch (a little micro switch) arcs at the tiny contacts. After a while, they become burned and are not able to complete the circuit that tells the oven the door is closed . . . door open, no heat. (forget what you know about the door being closed, the oven needs to kow)
2) There is a capacitor in your machine. They are very dangerous to work on if you do not understand their operation and the danger they represent. A capacitor stores power necessary to start the magnatron, the device that allows the heat process to begin. If mis-handled they can be lethal.
3) The mangnatron can be bad. This is extremely rare.
There may be other reasons for no heat complaint but lets deal with the first one first.
Remove the cover - don't touch the silver can (the capacitor) Look for the micro switches that are the door safety interlock. Find them opposite the hinge. Test them with a volt/omh meter. With the door closed the switch contacts should read closed. On some ovens, there are multiple switches and on some ovens one of the switches may read open. You will have to examine the switchs to see what they should be doing when at rest (normally open or normally closed).
If you cannot determine normally open or normally closed, you can still check the switches. If the door is open and the switch reads OPEN (the position of the contacts - no signal can pass open contacts), close the door. If it still reads OPEN - that switch is probably bad. Test all the switches (I have seen as many as three switches making up the safety device)
Modern capacitors are supose to drain their power within a certain amount of time rendering them safe to work on. There are many warnings against shorting the contacts of the capacitor to ground with a screw driver. The reason is it is a dangerous procedure unless done correctly (dangerous to the person holding the screw driver and possibly harmful to the oven).
A microwave repairman told me many years ago to use insulated pliers and remove the leads and reinsert them on to the terminals. He said this is frequently the reason the capacitor appears to be dead. He then did the procedure on my microwave and charged me $100.00 for the service call. The machine continues to work fine these many years later.
If your switches are fine and your capacitor is good (they are replacable (though dangerous if not handled with care)) the remaining main item is the magnatron. Unless you have a very expensive machine, it is probably not economical to repair this item.
You can find replacement parts at a FixYa.com advertiser or a appliance parts place in your area or visit www.repairclinic.com
I hope I have answered your question and I hope you are able to get your oven going again. I don't know what we would do without our microwave! You probably feel the same.
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