Before you call
Microwave runs but does not heat
This guide is shorter than the others on purpose. A microwave that turns and lights up but does not heat has a high-voltage fault, and the inside of a microwave is genuinely dangerous. There are only a few things worth checking, and then you stop.
Safety
Never remove the outer casing of a microwave. The capacitor inside holds a charge that can kill long after the unit is unplugged, and it does not need to be plugged in to do it. This is not the usual caution about voiding a warranty.
- 1
Heat one cup of water for one minute and see whether it warms at all.
Slightly warm is a different fault from completely cold, and it is worth knowing which you have. Never run a microwave empty — with no load the energy has nowhere to go and it damages the magnetron.
- 2
Check the door closes squarely and the latch clicks home.
Microwaves have several interlock switches, and one that has drifted out of adjustment will let the unit run without allowing it to heat. A door that has been slammed for years, or a latch with a broken tab, is a common and repairable cause.
- 3
Look at the waveguide cover on the inside wall.
It is a small mica panel, usually beige. If it is charred or has burned through, arcing has been happening and using the unit will make it worse. This is a cheap part but it is not a wipe-and-carry-on situation.
Where to stop
When to call a technician
Not for our convenience. These are the points where carrying on is either unsafe or makes the repair bigger.
- It runs and does not heat. Everything past the door switches is high voltage.
- You have seen sparking or arcing inside.
- There is a loud hum or buzz when it runs.
- The unit is over the range and also serves as the extractor — replacement is often the better answer, and we will tell you if it is.
An on-site diagnosis is $65.00, credited toward the repair if you go ahead. If this page has already fixed it, better still — you owe us nothing.