LG F9 Error: Oven Maximum Preheat Time Exceeded
Troubleshoot LG range error code F9 (preheat timeout).
Oven preheat timeout error. The control board monitored cavity temperature during preheat, but temperature failed to exceed 150°F within 5 minutes or failed to reach setpoint within 30 minutes.
Probable Causes
Burned out hidden bake element or rear convection heating element.
Stuck open heating relay on the electronic oven control (EOC) circuit board.
One 120V line of the 240V split-phase breaker tripped, providing only 120VAC to range.
Diagnostic & Testing Steps
- •Oven chimes error melody and displays F9 code after 15 to 25 minutes of preheating.
- •Bake element does not glow red; oven cavity remains barely lukewarm.
- •Food remains unbaked or takes twice the normal time to cook.
Tools & Equipment Required
- ✓Digital Multimeter (Resistance Mode)Measure heating elements: Bake element (18 - 25 Ω), Broil element (14 - 20 Ω), Convection (18 - 24 Ω).
- ✓1/4-inch Hex Nut Driver & Phillips #2Remove range rear protective metal cover to access heating element terminal spade lugs.
- ✓Insulated Work GlovesHand protection while handling sharp galvanized steel sheet metal panels.
- ✓Inspection FlashlightInspect heating element ceramic insulator bushings for cracks or burn marks.
Fast Reset Sequence: LG Electronic Hard Power Reset
Before unmounting panels or beginning diagnostic procedures, attempt this manufacturer reset to clear transient microcomputer lockouts:
- 1.Press Power to switch the machine off.
- 2.Unplug the unit from the electrical wall outlet.
- 3.While completely disconnected, press and hold Start/Pause for 5 seconds, followed by holding Power for 5 seconds.
- 4.Plug unit back in, select Drain/Spin mode, and verify that the control relay clicks properly.
- 1
Step 1: Verify 240VAC Split-Phase Voltage at Terminal Block
[ ] DoneTest AC voltage at range power cord terminal block: L1 to L2 must read 240 VAC; L1 to Neutral and L2 to Neutral must read 120 VAC.
Verification:Full 240 VAC is present; rules out a single-phase utility or breaker failure. - 2
Step 2: Test Hidden Bake Element Ohmic Resistance
[ ] DoneUnplug range, remove rear metal backplate, disconnect one wire lead from bake element, and test ohms across posts.
Verification:Healthy element measures 17 to 20 Ω. Reading of infinity (OL) confirms burned element. - 3
Step 3: Inspect Relay Board Solder Joints and Reassemble
[ ] DoneInspect main PCB relays (marked BAKE and BROIL) for black burn marks or melted solder pins.
Verification:Relay board has intact solder traces. Replace element or PCB; run 350°F test bake.
Repair Solutions
Check 240V circuit breaker at main panel: verify both poles are clicked firmly ON.
Remove rear cabinet panel and test heating element resistance with a multimeter (16–22 Ω).
Test for 240VAC across bake element terminals during an active Bake demand.
Frequently Asked Questions
Why does my LG range cooktop work fine while the oven shows F9?
Surface burner control switches operate on independent circuits, while the oven relies on high-current 240V heating relays and temperature sensors.
What is the ProBake element on LG ranges?
LG ProBake models eliminate the bottom floor element and place the primary 3,200W heating element around the convection fan on the rear wall.