Microwave Not Heating

• Failed magnetron — The magnetron is the tube that turns electricity into microwave energy, and a failed one can leave the microwave running, lit and turning the plate without heating.
• High-voltage diode or capacitor fault — In transformer models these two parts double the voltage that feeds the magnetron, and a shorted diode or a failed capacitor cuts the heat, sometimes with a loud hum.
• High-voltage transformer or inverter board — A transformer with a burnt winding stops the heat and can leave a burning smell. Inverter models use one power board in place of the separate transformer, capacitor and diode, and a failed board stops the heat too.
• Door interlock switch — The microwave heats only while its door switches report the door shut, and a worn switch can let the light and plate run while the heating circuit stays off.
• Thermal protector — A heat cutoff near the magnetron or the cavity opens when the parts run too hot, for example after the vents are blocked or the cooling fan stops.
• Control board relay — The control switches the high-voltage circuit through a relay, and a relay that no longer closes leaves the timer, light and plate working with no heat.

• Light, fan and turntable work but food stays cold — The heating circuit is off while everything else runs, which points to the magnetron, the high-voltage parts or a door switch.
• A loud hum or buzz and no heat — A shorted diode or capacitor, a failing magnetron or a transformer under strain, so stop running it until it is checked.
• It heats for a short while and then stops — A thermal protector cutting the power because the parts run too hot, so check that nothing blocks the vents and that the cooling fan runs.
• Food takes far longer to heat than it used to — A weakening magnetron, or a power level that was left set low.
• A burning smell or scorch marks near the vents — A failed high-voltage part or burnt wiring, so stop using it, unplug it or switch off its breaker, and keep the door closed if there is smoke inside.
• The display shows a demo word or symbol — A store demo mode runs the timer, light and plate without heat, and the use and care manual shows how to switch it off.

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