How to Replace the Waveguide Cover on a LG LMV1831ST Microwave — Step-by-Step Instructions
Step-by-step instructions for the LG LMV1831ST (over-the-range microwave, 1.8 cu ft). Parts and access points can differ slightly by production year — the steps below cover the common layout for this platform, and the model notes flag its quirks.
Cavity-level work only, with the microwave unplugged. Never remove the outer metal cabinet of a microwave. The high-voltage capacitor inside stores a charge that can kill you, and it holds that charge after the unit is unplugged. Every step in this guide stays outside the cabinet or inside the cooking cavity — if a repair needs the case off, it is a job for a technician. Do not run the microwave with the cover removed — splatter will reach the waveguide and damage the magnetron.
Tools
- Scissors or craft knife
- Small screwdriver
- Pencil
- Fine sandpaper (optional)
Parts
- Universal mica waveguide sheet $5–$15, or a model-specific cover $10–$30
Step by step
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1 Unplug the microwave
Then open the door and let any heat out.
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2 Photograph the old cover in place
Orientation matters, and the screw positions are easier to copy than to remember.
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3 Remove the old cover
Undo the one or two small screws, or release the tabs from their slot. Some covers slide sideways rather than pulling straight off — do not force it.
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4 Trace the shape onto the new sheet
Lay the old cover on the mica sheet and draw round it with a pencil, marking the screw holes and any notches.
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5 Cut and finish the new cover
Cut just outside the line with scissors or a craft knife. Mica cuts cleanly but flakes at the edge — a light pass with fine sandpaper tidies it. Punch or drill the screw holes rather than tearing them.
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6 Test fit before fixing
Offer it up and check it covers the opening completely with no gap at any edge. Trim if needed.
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7 Fit it and test
Screw or clip it in, plug back in, and run a cup of water for a minute. Watch through the door — no flashes, and hot water at the end, means the job is done.
🔧 Hand-off point: If the new cover chars again within weeks, something behind it is wrong. Repeatedly replacing burned covers masks a magnetron or waveguide fault that needs a technician. find a microwave repair pro near you →
LG LMV1831ST notes & error codes
The EasyClean cavity coating should never meet an abrasive pad or oven cleaner. Once it is scoured through to bare metal the cavity arcs on the exposed steel, and a cavity arcing on bare metal is the end of the appliance rather than a repair.
| Code | What it means |
|---|---|
| F3 | Key stuck on the touch panel |
| F5 | Humidity sensor fault |
| F7 | Control communication error |
Full details for this machine — common problems, causes, and costs — are in the LG LMV1831ST repair guide. The general version of these instructions is here.
If a fresh cover chars again quickly, something else is wrong — usually a magnetron antenna problem or damage inside the waveguide. Repeated burning of new covers is a stop-and-call-someone symptom, not a consumable to keep replacing. If you'd rather skip it entirely, find a microwave repair pro near you →
What this repair costs professionally
Sources
Where the safety, regulatory and warranty claims on this page come from. Repair costs are our own figures based on Arizona market rates and OEM parts pricing.
- Microwave Ovens — Radiation-Emitting Products U.S. Food & Drug Administration The federal requirement for two independent door interlocks plus a monitoring system, and the 21 CFR 1030.10 leakage limit — why an interlock must never be bypassed.
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