Microwave runs but does not heat; display shows E3 after a few seconds of operation.

Critical Safety Warning: The high-voltage section of a microwave (transformer, capacitor, diode, magnetron) can store and generate lethal voltages. Do not attempt internal high-voltage repairs unless you are qualified and know how to safely discharge the capacitor.

User-level checks:

• 1. Confirm symptom: Place a cup of water inside and run for 1–2 minutes. If the turntable, light, and fan operate but the water remains cold and E3 appears, the issue is in the high-voltage circuit.
• 2. Power reset: Unplug for 10 minutes, then retry. If E3 returns, internal components are likely faulty.

Technician-level checks:

• Unplug the microwave and remove the outer cabinet.
• Discharge the high-voltage capacitor using a proper resistor and insulated tools.
• Inspect the high-voltage transformer for burning, melted insulation, or a burnt smell.
• Test the high-voltage diode with a multimeter capable of diode testing; replace if shorted or open.
• Test the high-voltage capacitor for capacitance and leakage; replace if out of spec or shorted.
• Check any internal high-voltage fuse or thermal fuses in the HV circuit and replace only with identical rated parts.

Recommendation: Due to the danger and complexity, most users should have a professional service the high-voltage system on Tower microwaves.