It runs, it just stays cold
A microwave that will not heat can still look alive. The plate turns, the interior light comes on, the fan hums, and the timer counts down. The food stays cold. That split is the most useful clue.
It suggests that the controls and low-voltage side are working while the high-voltage circuit that generates microwave energy is not.
The three usual suspects
The magnetron. This part produces microwave energy. When it fails, the unit can operate normally with zero heat. A magnetron often lasts eight to ten years. A loud buzz may appear before failure.
The high-voltage diode. The diode helps raise voltage for the magnetron. A failed one can leave the unit running without heat, blow a fuse, or create a buzz or burning smell.
The high-voltage capacitor. The capacitor works with the diode and magnetron. It is a safety reason to keep the cabinet closed.
A fourth possibility is a door interlock switch. The unit refuses to heat if it cannot read the door as fully closed. A worn switch or cracked holder can create a no-heat symptom even when the high-voltage parts are intact.
What you can safely check first
- Run one cup of water for one minute. Never run the unit empty.
- Check the power-level setting. Level one or two heats slowly.
- Make sure the door closes flush and nothing blocks the latch.
- Unplug the microwave for sixty seconds, then test again.
If the water stays cold after those checks, the fault is internal.
Why this one is stop-and-call
The high-voltage capacitor can store a charge strong enough to injure or kill, even after unplugging. It must be discharged with proper equipment before the cabinet is safe to touch.
Do not remove the panel or test the magnetron, diode, capacitor, or transformer at home. For microwaves, replacement is usually the honest answer.
Repair or replace
Use the full replacement cost:
- Countertop under about $200 new: replacement usually wins because internal parts and labor add up.
- Over-the-range, built-in, or drawer unit: a typical Bay Area replacement can be about $600 to $1,500 after the unit and installation are considered.
- Microwave-convection combo or wall unit: cabinet fit and installation can make replacement more involved, but case-off work is still not DIY-safe.
If the microwave arcs, smokes, or smells like burning plastic, stop using it and unplug it at the wall.
Make the replacement decision
Microwave repair is not a service ADRIUM offers. For safe explanations of appliance symptoms and replacement planning, see the Home Service Pros information resource.
FAQ
Why does my microwave run but not heat? The low-voltage side works while the high-voltage circuit has failed. The magnetron, diode, or capacitor is a likely suspect.
Fix it or buy new? Replace a cheap countertop unit. For a built-in or over-the-range unit, compare the full installation and replacement cost.
Can I do it myself? Not safely. The capacitor holds a dangerous charge after unplugging.
What should I check first? Test a cup of water, confirm the power level, inspect the latch, and reset power for sixty seconds. Do not open the case.