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Microwave starts by itself or will not stop

A microwave that heats on its own is a fire hazard: unplug it and do not use it. The usual cause is a stuck relay or shorted triac on the control. On OTR units, a fan that starts by itself is often normal heat protection, and a light that stays on can be moisture.

Single source ~30 min advancedBrands: All

Before you start

  • Fire hazard: unplug immediately if the unit heats by itself
  • DANGER: the HV capacitor can hold a lethal charge even when unplugged; untrained users must not open the cabinet
  • Never test with the HV circuit energized

Diagnostic steps

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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Microwave starts by itself or will not stop · OnCall Tech