Microwave Keeps Running and Will Not Turn Off? Why

When a microwave keeps running and will not turn off, a switch or the control has stuck closed. Usually, a primary interlock switch stuck closed or a failed control board is the cause. First, unplug the unit at once, because running with the door open is unsafe. Then, test the switches and board below.

Safety first. Unplug the microwave before you open the cabinet. The high voltage capacitor can hold a lethal charge long after you unplug the unit, so it must be discharged before any internal work. Because of this shock hazard, leave the magnetron, high voltage diode, and capacitor to a qualified technician. Never run the microwave empty.

Parts to inspect for a microwave that keeps running

1. Door Interlock Switch

The primary and secondary interlock switches let the magnetron run only with the door closed, and they cut power the instant the door opens. When a primary interlock switch sticks welded closed, the microwave can keep running with the door open, which is unsafe. The monitor switch is the fail-safe that blows the line fuse if the primary switches do not open. So test each switch for a clean make and break as the door moves. Replace any switch that sticks or does not switch cleanly.

Unplug the microwave before you reach this part, and have the high voltage capacitor discharged first, since it can hold a lethal charge even when unplugged.

2. Smart Board

The control board, or smart board, runs the microwave and its relays. When a relay sticks closed, the unit can keep running or fail to shut off on command. Therefore, once the switches test good, inspect the board for a stuck relay and burnt spots. Replace the board if a relay no longer opens.

Unplug the microwave before you reach this part, and have the high voltage capacitor discharged first, since it can hold a lethal charge even when unplugged.

Unplug it right away

A microwave that keeps running is a safety issue. First, unplug the unit at once, because a primary interlock switch stuck closed can let it run with the door open. Then, do not use it until it is repaired. Because this fault involves the door safety switches, a qualified technician should verify the interlock system before the unit goes back in service.

Get the parts

We supply OEM and replacement parts in bulk. Browse the Appliance Parts catalog, or request a bulk quote for volume orders.

Is the microwave old or failing often? So weigh a repair against a new unit, and browse complete microwaves and more when a replacement makes more sense.

Most of the time, a microwave that keeps running traces back to one worn part. So replace it, then run a short test with a cup of water and confirm the fix.

In short, a microwave that keeps running means a stuck interlock switch or control board. Unplug it until it is fixed.