If your LG microwave vents keep running, there is no need to panic as a little prevention goes a long way in stopping this problem.
Over the Range LG Microwaves
LG microwave ovens installed above a stove's range are linked to the ventilation hood. If anything on the range becomes too hot, LG microwaves are designed to automatically turn the vents on low to disperse the heat out the ventilation system. This is both to protect the kitchen and the microwave itself. LG warns that the vent may stay on for up to an hour cooling the area before automatically turning off.
Over the Range Solutions
To prevent the vents on your LG microwave from continuing to run, do not over-boil or over-cook your food and use a cover on any pots and pans. A pot of boiling-over pasta uncovered can trigger the LG microwave vents, keeping them on until the sensors detect a noticeable change in temperature. Turn on the vents for a few minutes when opening a very hot oven or uncovering boiling foods to prevent triggering the automatic response. Of course, never leave your cooking food unattended to prevent over-cooking and burning.
Countertop LG Microwaves
Countertop LG microwaves also have vents, but instead of venting the hot air of something beneath it, the microwave vents any steam built up inside it. If too much steam builds up during the cooking period, the vents release the steam outside the microwave to prevent damage to the microwave oven. Over the range LG microwaves have this feature as well.
Countertop Solutions
First, ensure nothing is blocking the LG microwave vents. The vents will continue to run if partially blocked as they must work harder to vent the steam. Also, partially cover or poke hole in the packaging of food you are cooking in the microwave that cause a lot of steam. This will release the steam slowly into the microwave, allowing it to vent properly while helping your food cook faster.