Not Heating
LG Microwave
Severity: ModerateWhat Does This Error Mean?
An LG microwave that runs but does not heat has a fault in the high-voltage system — most commonly a failed diode, a blown thermal fuse, or a failed magnetron. These components carry lethal voltage even when unplugged. Do not open the casing — contact an LG-authorised technician.
Affected Models
- LG Over-the-Range Microwave
- LG NeoChef Countertop Microwave
- LG LMV Series
- LG LMVH Series
- LG LMC Series
Common Causes
- Failed high-voltage diode — converts AC power to the voltage the magnetron needs
- Blown thermal fuse — a one-time safety fuse that cuts out after overheating
- Failed magnetron — the microwave energy generating tube
- Door interlock switch fault preventing heating circuit activation
- High-voltage capacitor failure
How to Fix It
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Confirm the microwave is definitely not heating.
Place a microwave-safe cup with 8 oz (250ml) of cold water inside and run on full power for 1 minute. If the water temperature has not changed at all, heating is confirmed as non-functional. If the water is slightly warm but not as hot as expected, the magnetron may be underperforming.
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Check the door closes fully.
LG microwaves have three door interlock switches that must all activate for heating to engage. Open and firmly reclose the door. Look for any cracks in the door hooks — a broken hook prevents interlock switch activation.
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Check whether any error code is displayed.
LG microwaves sometimes display an error code alongside a no-heat condition (F1, F3). Note any code and follow the specific code troubleshooting. No visible error code with a completely cold microwave points to a high-voltage component failure.
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Do not open the microwave casing yourself.
The LG microwave high-voltage capacitor holds up to 2,100 volts DC — enough to cause fatal electrocution — and retains this charge long after the unit is unplugged. Only a qualified appliance technician with proper discharge tools should diagnose and replace high-voltage components.
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Contact LG service or an appliance repair technician.
LG customer service (1-800-243-0000) can arrange an authorised service visit. For LG microwaves under 1 year old, the fault is covered under warranty. For older units, a technician will diagnose the specific failed component before quoting a repair cost.
Frequently Asked Questions
Is it worth repairing an LG microwave that stopped heating?
For an LG microwave under 5 years old, a diode or thermal fuse replacement (typically $80-150 total) is usually worth it. Magnetron replacement costs $150-300 and is borderline for mid-range units. For an over-the-range model, repair tends to be more worthwhile because the installation cost of a replacement is significant.
Can a thermal fuse blow repeatedly on an LG microwave?
A thermal fuse is a one-time device — once blown it must be replaced, it cannot reset. If a new thermal fuse blows again quickly, something is causing the microwave to overheat — typically blocked ventilation or a failing magnetron drawing excess current. The root cause must be found and fixed, not just the fuse replaced repeatedly.