The Most Common Causes
These are the failure modes our technicians see most often on this symptom — listed in rough order of frequency. We don't publish step-by-step repair instructions for liability reasons, but the diagnostic process below identifies which one applies to your machine before any parts get swapped.
Failed magnetron
The tube that generates the microwave energy. Burns out after 5–10 years of heavy use. Most common cause of 'runs but no heat.'
Failed high-voltage diode
Rectifier that feeds the magnetron. Cheap part but high-voltage handling required.
Failed high-voltage capacitor
Stores the high voltage. Capacitors can retain lethal charge even when unplugged — never touch one without proper discharge tools.
Failed transformer
Less common but the most expensive of the high-voltage failures. Replacement may push toward replacement of the unit itself on lower-end models.
Failed thermal cutoff
Safety device that opens if the magnetron overheats. Cheap part.
Before You Call — What's Safe to Try
Some of this you can absolutely handle, and we'll tell you straight which parts. Other fixes are doable but carry real risk, and a few you should never touch. This is general guidance, not professional advice — always unplug the appliance (or shut off the gas/water) before you check anything, and if it feels beyond you, that's exactly what the $50 Quick Check is for.
✅ Safe to try yourself
- Confirm the door closes fully. A door not latching all the way stops the microwave from heating as a safety feature. Press it firmly shut.
- Check the mode. Make sure you are not on a timer-only / kitchen-timer setting instead of cook.
- Run the water test. Heat a cup of water for one minute — if it warms, the unit works and the issue may be how dishes are loaded.
🛑 Call a pro — don't touch this
- HARD STOP — do not open a microwave. The high-voltage capacitor can hold a LETHAL charge even when unplugged. The magnetron, diode, and capacitor are genuinely dangerous. If the safe checks above do not fix it, have a pro look at it or replace the unit.
The Honest Answer
Depends on age and model. Countertop microwaves under $200 usually aren't worth $300+ repairs. Over-the-range and built-in microwaves are almost always worth fixing — replacement is a major install. The TDR shows you the math. Parts availability and labor complexity matter more than the age of the machine. A well-built ten-year-old appliance with an available part is often worth fixing twice. A newer unit with a discontinued board is the harder call. Our techs lay both options out side-by-side — repair cost vs. replacement cost — and let you decide. Try the replacement calculator for a quick framing, but every situation is different.
Where's My Model Number?
A real technician needs your model number to nail the diagnosis and bring the right part. Here's where it hides — snap a photo when you find it.
Need the Part? We'll Find It.
Tell us your model and what's wrong — we identify the exact part, confirm it fits, and ship it to your door or install it. No hunting for part numbers; that's our job.
The 4-Option Technician Decision Report
After your $50 Quick Check (or $100 in-home diagnostic), a real technician — not a chatbot — reviews your model, video, and symptoms. They build a Technician Decision Report with four honest options:
You pick which option works for you. No surprises, no hidden costs. We don't share specific part numbers — we source the parts ourselves and ship them directly to your door, so you never have to hunt for the right SKU.
Real Numbers, No Mystery
Most repairs for this symptom land in the range below. The diagnostic confirms exactly which job it is before any quote — and the diagnostic fee credits toward your repair labor.
People Also Ask
Other Things That Could Be Wrong
Middle TN + Louisiana
Whether you're in Nashville or Hammond, the diagnostic process is the same. We service Middle Tennessee and Louisiana with six experienced technicians.
Outside the cities listed? Chat with Ant — we'll confirm coverage before you pay anything.
Chat with Ant — Get a Real Answer Today
Chat with Ant — tell us what's wrong, share a quick video and your model number photo, and a real technician will build your Technician Decision Report. No hold music, no guessing, no commitment until you see your options.