A built-in microwave that runs — light on, fan going — but doesn’t actually heat food is one of the more common — and one of the more technician-bound — appliance complaints, but a couple of things are worth ruling out first.
What usually causes it
- The door or drawer isn’t closing fully, which trips a safety interlock and stops the magnetron from running
- A failing magnetron (the component that actually generates heat) — the most common cause of “runs but doesn’t heat”
- A blown high-voltage fuse or diode
What you can check yourself
- Make sure the door or drawer is closing fully, and nothing (a container edge, a warped door, something caught in the drawer track) is keeping it from seating
- Confirm you’re not accidentally on a “keep warm” or low-power setting
- That’s genuinely the extent of what’s safe to check yourself
When to call
⚠️ This is the one appliance here where we don’t recommend opening anything up, even to look. Built-in microwaves store high-voltage electricity in their capacitors even after the power is off — that’s a real safety hazard, not caution for its own sake. If the door or drawer closes fully and it still doesn’t heat, that’s a call.