Microwave will not start; display works but pressing START does nothing or beeps three times

Safety first: Unplug the microwave from the mains. Microwaves contain high-voltage components that can retain a charge even when unplugged. Do not touch the high-voltage capacitor or magnetron area unless you are trained.

Step-by-step checks:

• 1. Inspect the door and latch: Open and close the door several times. Check that the door sits evenly, the latch hooks are not cracked, and the door closes with a firm click. If the door is sagging, gently lift while closing to see if the unit will start (indicates misalignment).
• 2. Check for stuck or loose door switches: With the unit unplugged, remove the outer cabinet (usually screws at the back and sides). Locate the door interlock switch cluster near the door latch. Inspect for broken plastic mounts, loose screws, or burnt connectors.
• 3. Test door switches with a multimeter: Remove one wire at a time from each switch. Set the meter to continuity (beep) mode. For the primary and secondary interlock switches, you should have continuity when the door is closed and none when open. Replace any switch that does not change state correctly.
• 4. Check wiring harness: Inspect the small harness that connects the switches to the control board for burnt, loose, or broken wires. Reseat connectors firmly.
• 5. Reassemble and test: Refit the cabinet, plug in the microwave, and test with a cup of water. If the unit still will not start, the control board may also be involved and professional service is recommended.

Warning: If you are not comfortable working around high-voltage appliances, contact a qualified technician.