LG Cooktop Error Code F9

F9 indicates a fault in the right inverter heat sink thermistor circuit. The cooktop's control system monitors this thermistor to protect the inverter electronics from overheating. When the thermistor's resistance falls outside the expected range of 45 to 55 K ohms at room temperature, the unit displays F9 and disables the affected cooking zone.

The cooktop disables the affected right cooking zone when F9 is active, which is a protective measure to prevent damage to the inverter electronics. You should not attempt to bypass this shutdown. The cooktop should not be used until the fault is diagnosed and repaired, as continued attempts to operate it could cause further damage to the inverter board.

If only the thermistor requires replacement, parts and labor costs typically range from around 80 to 200 dollars depending on your location and the technician's rates. If the inverter board itself has failed, repair costs can range from 200 to 450 dollars or more, since inverter boards are more expensive components. Getting a diagnosis before committing to a repair is a good idea, as the cost of the board may factor into the decision to repair versus replace.

A knowledgeable DIYer comfortable working with electronics can perform the initial diagnostics by checking the resistance at connector CN 02 with a multimeter. If the thermistor is the issue, replacing it is a moderately involved repair requiring disassembly of the cooktop. Work involving the inverter board should be handled carefully, as capacitors on the board can retain a charge even when unplugged.

Cycling power to the cooktop may temporarily clear the display, but F9 will return as soon as the control system re-reads the thermistor signal if the underlying fault has not been corrected. A reset does not fix the defective thermistor, wiring, or connector causing the code. The fault must be properly diagnosed and repaired to resolve the error permanently.