Stop using the appliance and cut its power at the breaker. Sparking, arcing and a burning smell are the three symptoms on this site that are never worth one more cycle. Inside a microwave, arcing is usually a burnt waveguide cover or metal in the cavity; at an electric cooktop it is a receptacle overheating under load; and grease dripping from a range hood means the duct is carrying a fire load. None of the three gets better on its own.
Read this first
- A microwave's high-voltage capacitor can hold a charge capable of killing you long after the plug is out. Do not open the cabinet under any circumstances.
- If flames appear inside a microwave or oven, keep the door shut, switch it off, and pull the plug or breaker if you can reach it safely. Opening the door feeds it air.
- Never use water on an electrical or grease fire. If it is not out immediately, get everyone out and call 911.
- Grease in a hood duct is a fire load. A dripping hood is not a cosmetic problem and should not wait for a convenient weekend.
- If you smell gas rather than burning, leave the building and call the gas utility or 911 from outside. Do not touch switches on the way out.
What it usually means
Arcing is energy going somewhere it was not designed to go, and the damage compounds fast. A microwave that arcs off a carbonised waveguide cover will burn a hole through the cavity wall within a few uses, at which point the repair stops being a roughly $10 cover. A cooktop receptacle that has started to scorch is a poor connection generating heat under a 240-volt load, and poor connections do not recover — they get hotter.
The grease case is different in kind. A range hood that drips is telling you the filters stopped capturing grease some time ago and the blower, the duct and possibly the roof cap are now coated. That is not a performance complaint, it is a fire load sitting in the ceiling above a cooktop, and it is the reason commercial kitchens have scheduled duct cleaning.
What to check first
Cut the power at the breaker
Not the switch and not the front panel. If an appliance has sparked, arced or produced a burning smell, isolate it properly before doing anything else, and leave it isolated until it is fixed.
Look for the obvious cause in a microwave cavity
Metal trim on a dish, a twist tie, foil, or a fork left in a container causes arcing that is entirely your dinner's fault and not a fault at all. Remove it, wipe the cavity, and try again with a cup of water.
Inspect the waveguide cover
The small mica or plastic panel on the cavity's side or ceiling. If it is stained, blistered or has a burnt hole, that is your arc source. It is a genuinely cheap part, but a cavity wall that has burnt through underneath it is not repairable.
Check an electric cooktop receptacle for scorching
With the breaker off, pull the coil element and look at the socket. Brown, black or melted terminals mean the connection has been running hot. Replace the receptacle and pigtail as an assembly — never clean up burnt terminals and reuse them.
Pull the range hood filters and look past them
Hold each filter up to a light. If they are saturated, grease has been getting past them into the blower housing and the duct for a while. Check the blower wheel and the duct collar for build-up.
Smell-test the difference between hot dust and burning insulation
A brief hot-dust smell on the first use of an oven or a heater each season is normal. A sharp, acrid plastic or fishy smell is overheating insulation or a failing component, and that one means power off and a technician.
DIY, technician, or licensed trade?
This is about who is allowed to do the work, not how hard it is. The bottom row is not a difficulty rating — it is the legal and safety line, and it does not move for confidence or experience.
- Removing metal objects from a microwave cavity and cleaning off food residue
- Replacing a microwave waveguide cover with the correct mica sheet
- Degreasing range hood filters, the grease cup and the blower housing with the breaker off
- Replacing an electric cooktop receptacle and pigtail after arcing damage
- Replacing a range hood blower motor or wheel
- Assessing whether a microwave with a burnt cavity wall is repairable at all
- All microwave high-voltage work — the capacitor can hold a lethal charge with the plug out
- Any scorched or overheating branch circuit, outlet or fixed wiring
- Cleaning or reworking a hood duct that runs inside a wall or ceiling cavity
Likely parts and what they cost
Our estimates for a typical US job, not quotes. “Part only” is what the component costs bought online against a model number; “installed” adds a technician’s diagnostic and labor.
| Part | Part only | Installed | Notes |
|---|---|---|---|
| Microwave waveguide cover | $6–$25 | $120–$250 | Cheap, and the fix for most arcing — provided the cavity wall behind it is intact. |
| Cooktop receptacle and pigtail kit | $20–$60 | $130–$280 | Always replaced as an assembly. Reusing burnt terminals restarts the problem. |
| Range hood grease filters | $15–$65 | n/a — DIY | Washable metal filters go in the dishwasher; replace them if the mesh is crushed. |
| Professional hood and duct degreasing | n/a — service | $200–$600 | The right call once grease has passed the blower into the duct run. |
| Microwave replacement | $120–$400 | n/a | Often cheaper than a magnetron repair on an older over-the-range unit. |
Prices are general estimates for typical US jobs, not quotes. What you actually pay depends on your appliance's brand and age, the part required, your region, and each shop's labour rate. Get the model number off the appliance before ordering — the same part varies in price across models.
Step-by-step guides for this symptom
3 guides cover this fault across 3 appliance types. Each one works through it in diagnostic order, with tools, parts and the point at which it stops being a DIY job.
- 15–30 minutesMicrowave
Microwave Sparking Inside — Stop and Fix It Before Using It Again
Arcing inside a microwave is usually a burnt waveguide cover, chipped cavity paint, or metal in the oven. Here is how to identify and fix each cause safely.
- 20–60 minutesOven & Range
Electric Burner Not Working — Coil and Smoothtop Diagnosis
One burner dead or weak on an electric range? Swap-test coil elements, check the receptacle for arcing, test the infinite switch, and check dual-ring selectors.
- 60–150 minutesRange Hood
Range Hood Dripping Grease — Fix the Cause, Not the Drip
Grease running down the hood or dripping onto the cooktop means saturated filters or condensate in the duct. Clean the system properly and stop the cause.