When a microwave quits heating, the repair-or-replace call usually comes down to one number: how much is the fix against what a comparable new unit costs. For most countertop models, if the repair runs past half the replacement cost, replace it. Under that line and the unit’s less than eight years old, repair usually wins. The catch is that you don’t know the number until someone finds the fault, and the fault could be a $20 switch or a $300 magnetron.
Why It Stopped Heating, Most Likely First
The magnetron makes the microwave energy. It’s the most common reason a unit runs, spins the plate, lights up, and produces no heat. It’s also the priciest single part to replace. On a $200 countertop unit, that math rarely pencils out.
Before anyone blames the magnetron, though, a tech rules out the cheaper suspects:
The door interlock switches. Most microwaves have three: primary, secondary, and a monitor switch. One stuck or failed switch cuts power to the magnetron while everything else keeps running. Switches are cheap, and they’re a very common failure point, especially on units that run hard every day.
The thermal cutout or thermoprotector. If the unit overheated at some point, a one-time thermal fuse may have opened. Cheap to replace if that’s the whole story.
The high-voltage diode and capacitor. Part of the circuit that steps voltage up for the magnetron. A failed diode is another common, affordable fix. The capacitor carries more risk, on cost and on the safety issue below.
The control board. Less common, but on touch-panel units a fried board can stop the cycle from starting even when the magnetron is fine. Depending on brand and model the board alone runs $50 to $150 or more before labor, and with a service call that can push a budget unit past the sensible line.
How a Tech Actually Runs It Down
A good tech doesn’t just swap the magnetron on the obvious guess. Step one is confirming the door switches work, because a bad switch is a far cheaper repair. After that the high-voltage circuit gets tested, confirming the diode, capacitor, and transformer are doing their jobs before condemning the magnetron.
That sequence is what decides whether a repair makes sense for you. A bad door switch is a sensible fix. A dead magnetron on a five-year-old $199 countertop unit is a different conversation, and an honest tech tells you straight: the parts cost more than a new microwave from the same tier.
What You Should Not Do Yourself
The high-voltage capacitor can store a lethal charge even when the unit is unplugged. This isn’t a be-careful note. It’s a real kill risk. Microwave capacitors can hold thousands of volts DC after you pull the plug, and they’ll discharge through you if you touch the terminals before they’re bled off. Even a cap with a built-in bleeder resistor can’t be trusted, because the resistor itself can fail.
Safe to check yourself: that the outlet has power, that the door closes and latches cleanly, and cleaning the waveguide cover if it looks scorched. Not DIY-safe: anything inside the cabinet touching the magnetron, diode, capacitor, or transformer. A tech discharges the cap with the right tool before touching anything, and that step is not optional.
The Decision, Laid Out
A rough framework:
Under 5 years, countertop, $300+ original cost: repair usually makes sense for a door switch, diode, or thermal fuse. Even a magnetron might pencil out.
5 to 8 years, mid-range ($150 to $300 original): repair makes sense for cheap parts. A magnetron is borderline. See the number first.
Over 8 years, or under $150 original: usually cleaner to replace. Parts get harder to find and the unit’s near end of life anyway.
Over-the-range and built-in units flip the math. A built-in that cost $600 to $1,000 installed is worth repairing even for a magnetron, because the alternative isn’t a $200 countertop swap, it’s the unit plus installation, possible cabinet work, and matching your kitchen. Same logic for a microwave-convection combo.
One more thing: if your microwave is arcing, sparks inside the cavity, stop using it now. Sometimes that’s just a scorched waveguide cover, a $5 to $15 part. Sometimes it’s deeper. Either way, don’t run it until someone looks.
When to Call
If the unit’s worth fixing by the framework above, get a diagnosis before you buy a replacement. A tech can usually tell you on the first visit whether it’s a cheap fix or a dead end.
Bay Area Appliance Repair Service covers the whole Bay Area. Call (925) 999-4095 or schedule a visit. The diagnostic is $75, credited toward the repair, and you get the price in writing before any parts are ordered. We’ll tell you straight if replacement makes more sense.