The short answer
Stop using the oven and unplug it for arcing inside the cavity, a burning smell, a breaker that trips, a damaged cord or any sign that it runs with the door open. Arcing usually has an ordinary cause such as metal or a damaged cavity wall, but it is diagnosed with the oven empty and off, never with the case open.
What you observe
- Sparks or flashes inside the cavity — Metal, foil trim or damage to the cavity surface.
- A burning or hot plastic smell — Stop at once and unplug.
- The breaker trips when the oven starts — A heavy load meeting a shared or weak circuit, or a fault.
- A cord or plug that is warm to the touch — A connection problem, and a fire risk rather than a nuisance.
- NEAR MISS - a hum and a bright cavity light on high power — Normal on most ovens.
Causes, most likely first on this brand
- Metal in the cavity — First for arcing. Foil, a metal-trimmed plate, a twist tie or a fork all arc, and on a combination oven the metal rack supplied for convection must not be used in a microwave-only mode.
- A damaged or heavily soiled cavity surface — Second. Burnt-on food or a chipped patch on the cavity wall or the waveguide cover concentrates energy at that spot and produces repeated arcing in the same place.
- A shared or overloaded circuit — Third for tripping. A microwave draws heavily, and on a kitchen circuit already carrying a kettle or a toaster it trips a breaker that is doing its job rather than failing.
- A damaged cord, plug or extension lead — Fourth. Heat at the plug means a poor connection, and an extension lead under this load is a common and avoidable cause.
- An internal fault in the high-voltage section — Last. Not an owner check under any circumstances, and the reason the case stays closed.
Check in this order, and why
- Stop and unplug at the first burning smell — Nothing on this page is worth a second test run.
- Look for metal, foil or a metal-trimmed dish — The commonest cause of arcing by far.
- Inspect the cavity wall and the waveguide cover — Repeated arcing in one spot marks its own cause.
- Plug the oven into a different circuit alone — Separates a shared-circuit trip from an oven fault.
What an owner can safely check
- Unplug the oven at the first sign of arcing or smell — Do not run it again to see whether it repeats.
About 5 min
- Remove all metal and check the dish — Look for metallic trim on plates, foil and twist ties.
About 10 min
- Clean the cavity thoroughly — Soften burnt-on food with a bowl of water heated in a known-good oven, then wipe it away.
Tools: cloth, warm soapy waterAbout 25 min
- Try the oven alone on a different circuit — Plug it straight into the outlet, never through an extension lead.
About 15 min
- STOP HERE for any scorch mark, damaged cord or repeat trip — Those are service matters.
Before you open anything
Safety
A microwave oven contains a high-voltage capacitor that can hold a lethal charge long after the oven is unplugged, so the case must never be opened by an owner - not to look, not to clean, not to check a fuse. Never defeat a door interlock. Never run the oven empty. Do not use an extension lead. If the oven runs with the door open, or arcs after a thorough clean, unplug it and stop using it.
When to call a technician
Call, with the oven unplugged, for any burning smell, any scorch mark inside the cavity or on the waveguide cover, arcing that repeats after a thorough clean with no metal present, a warm or damaged plug, or a breaker that trips with the oven alone on its own circuit. Do not keep resetting the breaker to see whether it holds, because repeated resets make a fault worse.
Nearest pages of this class
What this page does not cover
This page covers the Breville countertop microwave ovens as a class rather than one model family, and it deliberately stops at the case. Not included: internal component identification, capacitor discharge procedure, fuse ratings, leakage testing and circuit ratings - all of which belong to a qualified technician with the correct instruments.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
