Richard H Hudson , OH January 16, 2015 Appliance: LG Microwave Oven LRM1250W 01 Lg Microwave Lrm1250w / : My lg microwave was not heating i checked the electrical system and determined that the magnetron needed replacing. How to replace Magnetron. To me it wasn't hard to replace the magnetron having had the right tools. Once you have the cover off you just unscrew six screws on the magnetron and put the new one on. Do-It-Yourself Rating: Repair Time Estimate: 15-30 minutes