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Not Heating - Microwave

  • Troubleshooting

When the microwave oven does not heat, it may be caused by entering the wrong settings or an inadequate power supply. The microwave should display an error code if there is a severe problem which requires a technician. If there is no error code on your microwave's display screen, then let's troubleshoot.

Do you see any error code?

The first step, let's test the microwave:

  1. Did the keypad respond and the microwave start?

    Yes No
  2. Did the water heat after the test?

    Yes No
  3. If the keypad does not respond, it is possible that the CHILD LOCK feature is active.

    Child lock is a safety feature used to lock the control panel when cleaning the microwave, so that children cannot use the microwave unsupervised.

    How to test if the CHILD LOCK feature is activated or de-activated:

    • Press the STOP/CLEAR button on the microwave's keypad.

    • How to activate child lock:Press and hold the START/ENTER key for approximately 4 seconds until the L indicator or a lock icon appears in the display. If your model's STOP/CLEAR button does not have a lock indicator on it, please refer to your owner's manual to see if your unit has CHILD LOCK.

      Set Child Lock
    • How to de-activate child lock:Press and hold the START/ENTER key again for approximately 4 seconds. The L indicator or lock icon should disappear from the display.

      Deactivate Child Lock
    • If the controls are still not responding, attempt a reset on the microwave by unplugging the unit for 2-3 minutes. Plug the microwave back in an attempt to use the microwave again.

    If the keypad is now responding, test the microwave again, and proceed to the next step.

    Proceed to Next Step

    If the display is not working, or only some of the keys are unresponsive, the microwave will require a repair service. Please visit our Request a Repair page to request for a professional service.

  4. If the water did heat, there are three explanations about why the microwave is not heating as expected:

    • The power level might have been set too low.

    • The timer function could have been activated by mistake which does not heat the microwave, but only works as an alarm.

    • A wrong sensor cook settings may have been used.

    The power level is adjustable by pressing the power button on your microwave. To know more about power level, check the power level table below, or refer to the owner's manual of your microwave. Download a copy of your owner's manual from our Manuals and Document page.

    The nine power levels in addition to HIGH, provide a choice of the best level for the food being cooked. Listed below are all the power levels, examples of foods best cooked at each level, and the amount of microwave power being used.

    Power Level Microwave Output Use

    100 High


    • Quick heating many convenience foods, and foods with high water content, such as soups and beverages.
    • Cooking tender cuts of meat e.g. ground meat.



    • Heating cream soups.



    • Heating rice, pasta or casseroles.



    • Cooking and heating foods that need a cooking power lower than high (for example, whole fish and meatloaf) or when food is cooking too fast.
    • Reheating a single serving of food.



    • Foods that require special care; such as cheese and egg dishes, pudding and custards.
    • Finishing cooking casseroles.



    • Cooking ham, whole poultry and pot roasts.
    • Simmering Stews



    • Melting chocolate
    • Heating pastries



    • Manually defrosting foods, such as bread, fish, meats, poultry and precooked foods.



    • Softening butter, cheese and ice cream.



    • Keeping food warm.
    • Taking the chill out of fruit.



    • Standing time in the oven.

    NOTE: To change your power level, refer to your owner's manual for specific instruction for the model of your microwave.

    The timer function is sometimes mistakenly selected instead of cooking function. When the timer function is selected, the microwave only works as an alarm.

    A simple way to detect this is when your microwave's display shows a time counting down, but the oven is not cooking.

    Some microwaves are built with sensor cook; selecting the wrong setting for the sensor cook can affect the cooking time of the microwave.

    Sensor Cook cooks favorite foods without selecting cooking times and power levels. The oven automatically determines required cooking time for each food item. When the internal sensor detects a certain amount of humidity coming from the food, it tells the oven how much longer to heat.

    Quickstep to fixing sensor cook issues:

    • Deactivate the sensor cook or sensor reheat.

    When you deactivate the sensor cook or reheat, check if the microwave will cook with the expected heating temperature.

  5. Is time counting down at an accelerated rate?

    Yes No
  6. If the time is counting down at an accelerated rate, the microwave's demo mode may be active.

    To deactivate demo mode, unplug the microwave from the power outlet for 10 seconds and plug it back in. After plugging the microwave back in, try operating the unit once again.

  7. Is the microwave on a dedicated circuit breaker?

    Yes No
  8. If all the proper settings are being used, and there is no power supply issues. The microwave will require a repair service. For your convenience, You can visit our Request a Repair page for a professional service.

  9. It is recommended that Over the Range microwaves should be on dedicated circuit breakers with nothing else plugged in. If other products are plugged into the same outlet, microwaves often cannot get enough power. If the unit is not on a dedicated breaker, it will be necessary to contact an electrician for the power supply to be setup correctly.

Error codes help technicians to identify what may affect the microwave's functionality. Apart from door error code, it is advisable to request for a professional technician to fix any other type of error code on your microwave.

List of possible errors:

Error code Likely Failure Condition Tech Details


The door is slightly opened.

Something is preventing the door from closing properly.


Thermistor is open.

No heat or thermistor sensing error.


Thermistor short for cooking

No heat in 10 seconds after cooking starts.


Thermistor short after cooking.

Thermistor temperature does not go down after cooking ends.


Sensor open

Humidity sensor is sensing error.


Damper Switch

Damper switch is sensing error.

To remove the error code, let's reset the unit:

  1. Unplug the unit from the wall outlet, or trip the circuit breaker to cut power supply to the machine.

  2. Allow the machine to remain unplugged for 10 - 15 seconds.

  3. Restore power to the unit.

  4. Place a 8 oz. (microwave safe) cup full of water inside the microwave. Run a time cooked setting for 30 seconds. If the error code repeats itself, the microwave will require a repair service. Please visit our Request a Repair page for a professional service.

To purchase LG Microwave parts for repair:

Click Here

To request a repair:

Click Here
Author - Sanmi Ajanaku

Sanmi is a Home Appliance expert and author of this help library article. Please leave him feedback below about the page.

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