Microwave runs but doesn't heat? What it means
By the technicians at Maximum Appliance Repair. Updated
Important: never remove a microwave's outer cover. A microwave stores a high voltage charge inside, even unplugged. The checks below are safe; the repairs behind the panel are for a technician.
Safety first: unplug the appliance or switch off its breaker before you open panels, and shut off gas or water if you'll be near those lines.
1. Test it with water
Heat a cup of water for one minute on full power. It should be clearly hot. If it's barely warm, the microwave isn't producing full power.
2. Check for a demo mode
Some models have a demo or display mode that runs the light, fan and turntable without heating. The manual shows how to turn it off. This is common right after a new install.
3. Check the power level and settings
Make sure the power level isn't set low, and you aren't using a defrost or keep-warm setting by mistake.
4. Close the door firmly
A microwave has several door switches. If the door is out of line or the latch is worn, the microwave may run without heating, or stop and start. Look for a bent latch or a door that doesn't sit flat.
5. Plug a countertop model into its own outlet
Microwaves draw a lot of current. On a weak or shared circuit, power can sag. Try it on another kitchen outlet with nothing else running.
Sparking with metal inside is normal and means something metal is in there. Sparking with nothing metal inside often means a burned waveguide cover, a small panel on the inside wall, which a technician can replace.
When to call a technician
Call us if it still doesn't heat, if it sparks or buzzes loudly, or if it blows the fuse. The usual causes are the magnetron, the high-voltage diode or capacitor, or a door switch. We repair over-the-range, built-in and drawer microwaves. Countertop microwaves usually cost less to replace than to repair.