If the diode burns out, the magnetron won’t receive enough voltage to operate, preventing the microwave from heating. When the microwave door closes, the door switches actuate in sequence to ensure that the door is closed properly. If any of the door switches fails, the microwave will not start or heat.Click to see full answer. Also, why does my microwave keep running when I close the door?If your microwave continues running when you open the door, it may be a problem with the door interlock switch. A functioning door switch provides power to other components of the microwave and should interrupt power when the door is open.Secondly, why does my microwave not turn off? If your microwave oven doesn’t shut off until the door is opened, you may have a problem with the control board. If the control is defective it may not shut off a relay when the function is complete, and then opening the door to interrupt the power to the control would be the only way to terminate the cycle. One may also ask, why is my microwave turning on when I open the door? Answer: If a microwave starts running when the door opens, reset the power at the circuit breaker and retest. If the microwave continues to start when the door opens, turn off power at the circuit breaker, or unplug the unit until it is repaired. The unit running with the door open is a safety issue.Why is my microwave shutting off?If the microwave runs for a few seconds and then shuts off, the door switch might be defective or loose. Sometimes arching or overheating of door switches stops microwave from running efficiently. Some microwaves have a seal or gasket around the door. If the seal or gasket is broken, microwave shuts down.