Microwave Runs but Won't Heat

What usually causes it

• Door switches. Most microwaves have several door switches. One failing can stop heating or blow the main fuse.
• High-voltage diode. A common failure that stops heating.
• High-voltage capacitor. Can fail open or shorted.
• Magnetron. The part that makes the microwaves. It can wear out or fail.
• Thermal cutouts. These shut off the magnetron if it overheats, often because the vents are blocked.
• Control board. A failed relay on the board will not send power to the high-voltage transformer.

Microwave not heating

A microwave that runs but does not heat usually has a failed magnetron, diode or door switch.

Check first: Test with a cup of water for one minute.

Safe checks you can do

• Test with a cup of water for one minute. It should get noticeably warm.
• Check that the door closes firmly and the latch hooks are not broken.
• Make sure the vents on over-the-range models are not blocked.
• Do not remove the cabinet. Do not try to discharge the capacitor yourself.

Parts that fail most often

• High-voltage diodes and door switches are common causes of no heat.
• Magnetrons wear out after heavy use.

How your home affects it

In older homes

Older homes in the Houston area often have smaller kitchens and laundry closets built for smaller appliances, older wiring, and shut-off valves that have not been turned in years. Many older kitchens recirculate air instead of venting outside, so filters do all the work.

In new construction

Newer homes in the Houston area usually come with builder-grade appliances, and many early problems are installation issues rather than failed parts. Ducted hoods and over-the-range microwaves sometimes have a damper that was never opened.

In apartments and condos

In apartments, condos and townhomes around the Houston area, space is tight and the building often has its own rules for access, parking and shut-off valves. An over-the-range microwave or recirculating hood is often the only kitchen ventilation.

In garages

Plenty of homes in the Houston area keep a second fridge, a freezer or the laundry in the garage, where summer heat regularly passes 100°F. Outdoor kitchen hoods need weather-rated parts and regular cleaning.

During storm season

Storm season around the Houston area brings power outages, surges and sometimes flooding, and appliances often show problems right after the lights come back on. Surges can take out hood and microwave control boards; mention any recent outage when you call.

When to call for repair

• The microwave runs but does not heat water.
• You hear a loud buzz or hum during heating.
• The fuse blows when the door is opened or closed.

Do not open the microwave cabinet. If it sparks or smells burnt, stop using it.

Need help? We do microwave repair across Harris, Fort Bend and Montgomery counties. Call (832) 345-9300, Monday to Friday, 9 AM to 6 PM. Every repair comes with a 1-year warranty on labor.

Common questions