The short answer
Arcing, scorching, burning smells and a breaker that trips on cook are all reasons to disconnect the appliance now and leave it disconnected. None of them is a wait-and-see symptom, and none of the causes behind them is an owner repair.
Any one of these means stop
- Blue or orange flashes inside the cavity while cooking — Arcing. Stop the cycle and disconnect.
- Scorch marks on the waveguide cover or the cavity wall — Evidence of arcing that has already happened.
- A smell of hot insulation or burning plastic — Disconnect and do not use it again.
- The breaker trips whenever a cook cycle begins — A fault on the high-voltage side, not a nuisance trip.
- A plug or socket that is hot or discoloured — A supply fault that is a hazard in its own right.
- Not this fault: it simply does not heat, with nothing else wrong — That is the not-heating page.
What is usually behind it
- Food residue or a damaged waveguide cover arcing — The most common cause of cavity arcing, and it is why splatter should not be left to carbonise.
- Metal in the cavity, including decorated dishes — Common, avoidable, and capable of damaging the cover permanently.
- High-voltage component failure shorting to the chassis — The usual cause of a breaker that trips on cook.
- Grease accumulation inside a mounted chassis — Specific to over-the-range installations and a genuine fire consideration.
- Supply cord or socket degraded by heat — Fourth, and it presents as a warm plug before it presents as anything else.
- Cavity wall corroded through at the paint — Last, and it usually follows years of arcing nobody acted on.
What to do, in order
- Stop the cycle and disconnect the appliance — Before any investigation of any kind.
- Check for anything metallic or foil in the cavity — It explains many arcing events outright.
- Look at the waveguide cover for scorching or holes — A damaged cover means the unit stays out of service.
- Feel the plug and socket, carefully, for heat — A warm plug is an electrician’s job, separate from the appliance.
The safe sequence
- Press cancel, then unplug the unit or switch off its breaker — Disconnection comes first, always.
About 5 min
- Remove any metal, foil or metal-trimmed dish from the cavity — This is the one cause an owner can both find and eliminate.
About 5 min
- Clean carbonised splatter from the cavity and the cover face — Do it whenever it appears, because carbon is what arcs.
Tools: cloth, dish soapAbout 20 min
- Leave the appliance disconnected until it has been inspected — A unit that has arced once will arc again.
- Have the circuit checked if the plug or socket is hot — That is an electrician’s task and not an appliance repair.
The rules that apply here
Safety
Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off, and in a microwave that stored energy is lethal: the case does not come off, not to look, not to clean, not to photograph. Never run a unit that has arced, never operate it with a damaged waveguide cover, and never reset a breaker repeatedly to see whether it holds.
Call, and do not keep using it
Call a technician for arcing, for scorching, for a burning smell and for a breaker that trips on cook. Call an electrician instead if the plug, the socket or the circuit is the hot part. If you see flame in the cavity, keep the door shut, disconnect the power if it is safe to reach, and call the fire service: a closed door contains a small fire, and an open one feeds it.
Related pages
Scope
Generalized across families and written for mounted installations; the companion page covers counter-standing units. Where a family-specific or model-specific page exists it is the narrower answer. Deliberately not here: any internal test procedure, capacitor discharge method, component identification or wiring detail - all of which belong to a qualified technician and none of which makes this symptom safer to investigate at home.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
