There may be many reasons why the microwave oven doesn't heat, and the following are some common reasons:

1. There is something wrong with the baking net or tray: the baking net or tray may be damaged or destroyed, resulting in the microwave can't be transmitted or bounced, so that the microwave oven can't heat food.

2. Poor door seal: If the door of the microwave oven is poorly sealed, the microwave can escape from the crack of the door, resulting in the loss or non-transmission of microwave energy, thus causing the microwave oven to be unable to heat food.

3. lens or microwave tube failure: the lens or microwave tube may be excessively worn or broken after the microwave oven is used for a long time, resulting in microwave leakage or failure to drive, so that heating cannot be carried out.

4. Failure of high-voltage capacitor or switch: The high-voltage capacitor of microwave oven is responsible for storing radio energy, and the switch of microwave oven is used to cut off the high-voltage part of motor. If any of them breaks down, the microwave oven won't work.

5. failure of baking tube: when the baking tube is worn out or there are signs of arc discharge, the microwave oven can't emit more microwaves, so it can't heat food.

These are just some common reasons why microwave ovens don't heat up. Because of the complicated structure and limited service life of microwave ovens, it is necessary to avoid collision and collision during use, and regularly check and maintain them to prolong the service life of microwave ovens. If the cause of the failure cannot be determined, it is best to send the microwave oven to a professional maintenance unit for inspection and maintenance.