No heat I can hear microwave running but it just doesn't heat food.

see this causes and fix it. GOD BLESS YOU
Power Diode

A diode is an electronic component that readily passes current in one direction only and blocks the flow of current in the opposing direction. If your microwave's diode has become defective, your microwave will not heat and you will hear a buzzing noise. Test the diode to determine if this is the cause of your problem. Replace it if it is defective.

• How to test a microwave diode.
• How to replace a microwave diode.



• 
  

High Voltage Capacitor

A capacitor is an electrical device which stores electricity. A defective capacitor may be why your microwave is not heating but you are hearing a buzzing or humming noise. The capacitor will have to be tested to determine if this is the cause of your problem. A defective capacitor will have to be replaced before your microwave will work again. Make sure you discharge the capacitor before you test it, though.

• How to test a microwave capacitor.
• How to replace a microwave capacitor.



• 
  

Magnetron

A defective magnetron is the third possible cause of why your microwave is not heating, but you can hear a buzzing noise. Test your microwave's magnetron. Replace it if it is defective.

• How to test a microwave magnetron.
• How to replace a microwave magnetron.

Thermoprotector If the microwave doesn't heat the thermoprotector may have tripped. This is a safety device to prevent the microwave from overheating. It can be tested for continuity to see if it's blown.

Main Control Board If the microwave doesn't heat the main control board may be defective. This is not common. When a microwave doesn't heat the problem is usually within the high voltage circuit; either the high voltage capacitor, diode, transformer or magnetron.
High Voltage Transformer If the microwave does not heat, the high voltage transformer might be burned out. Microwave ovens produce a very high voltage in order to power the magnetron antenna, which emits the energy that cooks the food.

If the unit operates correctly except heating the food, then the unit needs a new magnetron.

There are a few possibilities, the magnetron is defective, or the high voltage capacitor or diode/or inverter board if microwave is under 7 years.

I would strongly consider replacing the microwave oven, prices have dropped considerably. The problem you are describing is in the keypad controller board.

If your microwave runs, but doesn'theat your food, verify that you have selected a cooking setting. You mayaccidentally set the timer. Test the magnetron by placing 1 cup of water in themicrowave and heating the water for three minutes. If the water doesn't heat,your magnetron is dead.

If your microwave runs, but doesn'theat your food, verify that you have selected a cooking setting. You mayaccidentally set the timer. Test the magnetron by placing 1 cup of water in themicrowave and heating the water for three minutes. If the water doesn't heat,your magnetron is dead.

The part of the oven called the "magnetron" (this part is what creates/generates the microwave energy that heats the food or liquid) is burned out, the cost to repair is more this part is more than the cost to replace with the cost of Microwaves so depressed by the stagnant economy.

The most likely cause is a defective magnetron, "heats food" cost to repair will be close to a new microwave oven.

if your microwave does everything you have described , and you can hear the cooling fan running as well after you press the start button , you probably have a faulty wave guide. The wave guide is also called a Magnetron Tube. It is the main part of the microwave which produces the microwave energy . If this part is not functioning it is best to replace the entire unit, rather than have it repaired .

No heat means the magnetron circuit has failed. It is the part that generates the microwaves to heat the food. Usually not worth fixing since the magnetron costs nearly as much as a new oven. To diagnose, if the oven is on, you will hear a loud buzzing sound if the magnetron is shorted.