Stop the microwave the moment you see sparking, and do not run it again until you have identified the cause. Most sparking has an obvious, fixable explanation — metal in the cavity, a damaged wave guide cover, or a build-up of food debris arcing against the cavity wall. All three are visible on inspection and resolved without opening the cabinet.
Stop it immediately
- Stop the microwave and unplug it
Press stop or open the door (which cuts power via the interlock switches), then unplug it from the wall.
- Do not run it again until you have checked inside
Repeated sparking can damage the cavity wall coating and the wave guide cover, turning an easily fixed cause into a more serious fault.
Common causes
| Cause | How likely | Typical sign |
|---|---|---|
| Metal object or metallic trim in the cavity | Very common | Twist ties, foil, metallic-rimmed plates or gold-trimmed dishes |
| Damaged wave guide cover | Very common | The small panel on a cavity wall, often scorched or with a visible hole |
| Food debris built up on cavity walls | Common | Splatter and residue that has carbonised over time |
| Empty or near-empty operation | Common | Running with nothing, or almost nothing, inside to absorb the energy |
| Damaged or worn cavity paint/coating | Occasional | Visible scratches or bare metal showing through the interior finish |
What to check
- Check for metal
Look carefully at whatever was inside, including plate trims, twist ties left on packaging, and any foil. Even a small amount of metal can cause sparking.
- Inspect the wave guide cover
This is a small mica or ceramic-composite panel, usually on a side or the top of the cavity interior, that protects the wave guide opening from food splatter. If it looks scorched, bubbled, or has a visible hole or burn mark, it needs replacing — this is a genuinely simple, inexpensive part on most models.
- Clean the cavity thoroughly
Wipe down all interior walls, paying particular attention to carbonised or built-up residue, which can arc against the cavity wall in the same way metal does.
- Never run it empty
Always have food or at least a cup of water inside when the microwave runs. Operating with nothing to absorb the microwave energy causes it to reflect and can damage the magnetron over time, beyond causing sparking.
- Test cautiously after addressing the cause
Once you have removed metal, replaced a damaged wave guide cover, or cleaned the cavity, run it briefly with a cup of water and watch closely. If sparking recurs with no metal present and a clean, undamaged wave guide cover, stop using it.
If sparking continues with no visible cause
Sparking that persists after ruling out metal, a damaged wave guide cover, and cavity debris points at an internal fault — most likely related to the magnetron or its mounting. This is inside the cabinet, and as with every microwave repair on this site, that is outside safe DIY territory because of the high-voltage capacitor.
If you have ruled out metal, a damaged wave guide cover, and food debris, and sparking still occurs, stop using the microwave entirely and have it assessed rather than continuing to test it.
When to call an appliance engineer
Call an engineer if sparking continues after checking for metal, replacing a damaged wave guide cover, and thoroughly cleaning the cavity. Given typical repair costs on this appliance, get a quote before committing, and weigh it against a replacement — see our microwave not heating guide for the same economic consideration.
Stop and call a qualified appliance technician or electrician if you find scorched or melted wiring, smell burning, see water that has reached electrical components, or if the fault returns immediately after a repair. Never bypass a safety device — thermal fuses, door interlocks and flood switches fail for a reason, and defeating one converts a broken appliance into a fire or flood risk.
