In short
Stop using the oven and unplug it first; then read the list. On this machine the most likely cause is metal, foil or a metal-trimmed dish in the cavity.
What you observe
- Sparks or a flash inside the cavity during a cycle — Arcing.
- A scorched patch on the waveguide cover at the side wall — Carbonised food on the cover, which then arcs against itself.
- A rust spot or chipped paint inside the cavity — Bare metal in a cavity arcs, and the oven should not be run.
- NEAR MISS — the light flickers but nothing else happens — A lamp or a socket issue rather than an arcing fault; check the supply first.
Causes, most likely first on a SharkNinja microwave
- Metal, foil or a metal-trimmed dish in the cavity — This is the commonest arcing cause by a long way, and it is over as soon as the item comes out. Ranked first on a SharkNinja microwave: the cavity is designed for food, so anything metallic in it will arc the first time the oven runs.
- Waveguide cover burnt or carbonised — The arcing then burns the cover further, so it gets worse with every cycle.
- A rack, turntable support or trim touching the cavity wall — Accessory racks are designed to stand clear; out of position, they arc against the wall.
- Chipped cavity paint or a rust spot — Rust usually starts at the bottom corners or around the waveguide cover screw.
Check in this order, and why
- Look at what was in the oven when it sparked — Check the plate as well: some decorative glazes contain metal.
- Look at the small panel on the cavity side wall for scorching or holes — Brown scorch marks or a hole in the cover is the fault.
- Check any rack or support is seated in its intended position — Remove the rack and run a test cycle on a cup of water.
What an owner can safely check
- Unplug the oven, remove everything from the cavity, and check the dish and any wrapping for metal — Foil, twist ties and metal-trimmed plates all arc. Remove them and inspect the cavity wall for burn marks.
About 10 min
- Unplug the oven and inspect the waveguide cover; wipe light splatter off it gently — A cover that is scorched, holed or soft is a replacement part — never run the oven without it.
Tools: soft cloth, torchAbout 15 min
- STOP HERE — the outer cabinet stays on — Everything past the cavity and the door is high-voltage work, and it is not an owner job at any point.
Before you open anything
Safety
Unplug the microwave before you touch anything beyond the cavity and the door. The outer cabinet stays on: a microwave holds a high-voltage capacitor that can retain a lethal charge long after the plug is out, and it is not an owner-serviceable machine. Never defeat, tape or bend a door interlock switch — those switches are the only thing that stops the magnetron running with the door open. Never run the oven empty, and stop using it altogether if the door will not close and latch properly.
When to call a technician
Call, and stop using the oven, whenever the arcing continues with a clean, empty cavity, whenever there is a burning smell, and whenever the breaker trips on a proven good socket. Foil and racks are owner fixes; a carbonised waveguide cover or a rusted cavity is not. Countertop machines are frequently cheaper to replace than to repair, so get the fault named before you pay for a diagnosis; check the warranty first, because most faults of this kind fall inside it.
Nearest pages of this class
What this page does not cover
This is the generalised SharkNinja microwave page. A family- or model-specific page, where one exists, is linked above and is the more precise answer for your unit. Left out on purpose: part numbers, connector colours, the order panels come off in, and every torque figure — a generalised page cannot be right about any of them.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
