Sparking inside the microwavewhat to check
Bright arcing and a scorched smell. Look at the small panel on the cavity wall before you run it again — a burnt waveguide cover is the usual answer.
Take care
What this means
Arcing in a microwave looks alarming and is usually caused by something you can see and reach. Start with the obvious: metal. Foil, a metal-trimmed plate, a fork left in a bowl, a twist tie, or the metal handle of a takeaway container will all produce sparks, and so will a china plate with a gilt rim. Take the metal out and the arcing stops. The second cause is the one people miss, and it is the reason this page recommends a specific place to look.
Set into the wall or the roof of the cavity is a small rectangular panel, usually a thin mica-coloured board, sometimes a plastic one. That is the waveguide cover, and it closes off the channel the microwave energy arrives through. It is not decorative and it is not optional. Food splashes onto it, the deposits carbonise, and carbon conducts — so the cover starts arcing against itself.
Once it has begun to burn through, the arcing gets worse each time, and the channel behind it is no longer protected from whatever is in the cavity. The distinguishing test is straightforward: metal-caused arcing happens where the metal is and stops when it is removed, while a failing waveguide cover arcs in the same spot every time, from a panel with visible brown or black scorching or a burnt-through hole. There is a third reason to take arcing seriously rather than tolerating it. Manufacturers list arcing damage to the door seal and the sealing surfaces among the checks to make on a microwave before it goes back to its owner, which tells you they regard sustained arcing as capable of compromising the assembly that keeps the energy inside the cavity.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Metal in the cavity | Foil, cutlery, a metal-rimmed plate or a twist tie. Arcs at the object and stops the moment it is taken out. | Common |
| Waveguide cover carbonised or burnt through | Food deposits on the panel char, and carbon conducts, so the cover begins to arc against itself in the same place. | Common |
| Baked-on food or grease on the cavity walls | Heavy carbonised deposits behave the same way as a dirty waveguide cover and arc without any metal present. | Occasional |
| Damage to the cavity coating exposing bare metal | Chipped enamel or a rust patch gives the energy an edge to concentrate on, and rust spreads once it starts. | Occasional |
What to try yourself
Stop the appliance and unplug it. Arcing is not something to watch to see whether it settles down.
Take everything out and look for metal — foil, a fork, a metal-trimmed plate, a bag tie, a takeaway container with a metal handle.
Find the waveguide cover. It is the small rectangular panel on the cavity wall or roof, often a thin board with a matt finish. Look for brown scorch marks, black spots, or a hole.
Clean the cavity properly, the cover included, with a damp cloth and washing-up liquid rather than anything abrasive. A cover that is only dirty will often stop arcing once it is clean and dry.
Let it dry fully before use. Do not scrub a mica board hard — it is soft and will delaminate, which turns a cleaning job into a replacement.If the cover is scorched through or holed, do not run the microwave until it has been replaced. It is an inexpensive part, and on many models a straightforward one, but the appliance should not be used with the channel open.
Get a qualified appliance engineer to look at your microwave
We do not pass enquiries to a repair firm, so there is no form here. When you book a qualified appliance engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What it costs to fix
Typical repair cost
£0–£120
Time on site
20 minutes
A waveguide cover is usually £5 to £20 as a part and often fitted from inside the cavity. With an engineer’s visit the job is typically £70 to £120, which on a cheap countertop machine is close to replacement cost.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related microwave fault codes
- Turntable not turningUsually simple to fixFood heats in patches and the plate sits still. Almost always the coupler, the roller ring or a plate seated wrongly, and mostly fixable in the cavity.Related: inside the cavity
- Not heating but runningGet it checkedThe light is on, the turntable is going round and the food comes out cold. This is the classic microwave failure and none of it is an owner repair.Related: same brand
- Microwave completely deadGet it checkedNo display, no light, no fan. On a microwave this is very often a safety system working as designed, and fitting a new fuse is the wrong repair.Related: same brand
- Is my microwave leakingGet it checkedThere is a published UK limit and a real test for this, and the door seal is what usually fails it. What there is not, is a way to check it at home.Related: same brand
- Ran the microwave emptyGet it checkedRunning a microwave with nothing in it is the one thing an owner can do that reliably damages it, and the service manuals put it in capitals.Related: same brand
- E01, E02 or E03 on an own-label microwaveGet it checkedOne inherited fault table printed under five UK badges. If your microwave shows E01, E02 or E03, the brand on the front is probably not who wrote it.Related: same brand
Related guides
Common questions
Can I use it if the arcing has stopped?
If the cause was metal you have taken out, yes. If it was the waveguide cover, no — the arcing will come back and get worse, because the cause is a burnt panel rather than an event. That is the point of identifying which one you had.
Can I replace the waveguide cover myself?
On many microwaves it is a genuinely accessible part inside the cavity, and covers are sold cut to size. Nothing about that requires opening the outer cabinet, which is the part that is not an owner job. Get the right part for the model rather than improvising with card or plastic.
Does sparking mean it is leaking radiation?
Not by itself. What is true, and worth knowing, is that manufacturers list arcing damage to the door seal and sealing surfaces among the safety checks to make before releasing an oven, so they treat sustained arcing as something that can damage the containment rather than as merely cosmetic.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.