Manual for model LMV1813ST - LG Over-the-Range Microwave

Could be magnetron failure but cooking a "foreign" object may have led to breakdown

The service manual for your model is here. That and my video here will give you disassembly info.

More questions? Contact me directly here.*

* always include the full model number and FCC ID number from the label on / in your microwave

F4 means sensor open, You have to check the Humidity sensor.
If you wish to get some details; visit the site linked here. Pull up older posts. http://electro-medical.blogspot.com/

The door switch and fuse will stop it from running.

If there was any odor, the cloud might have come from a failed component, such as the high voltage rectifier. That could blow the fuse.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/david_29ad5d1dd86564b0

If the control panel lights up intermittently, then you either have a loose connection somewhere near the panel, or a failing component on the circuit board itself.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/david_29ad5d1dd86564b0

http://kitchen.manualsonline.com/manuals/mfg/lg/lmv1813st_2.html

The fuse can be replaced, but the underlying issue should still be investigated and resolved. Otherwise the new fuse will blow also.
If the microwave is not working the thermal fuse may have blown.
When a microwave stops working the problem is usually the line fuse or within the high voltage circuit; either the high voltage capacitor, diode, transformer or magnetron.

replacemotor under microwave

Go for a warranty repair anyway. It may be the magnetron, and the clicking is the big condenser discharging.
https://www.lg.com/ca_en/support/warranty
Microwave Ovens (Over-the-Range):

• 1 year parts & labour
• 5 years on the magnetron (part only)

Microwave Ovens (countertop):

• 1 year replacement warranty
• 5 years on the magnetron (part only)