Microwave will not start; display is on but START button does nothing, sometimes accompanied by a brief relay click.

Safety first: Unplug the microwave and leave it disconnected for at least 10 minutes before removing any covers. Microwaves contain a high-voltage capacitor that can retain a dangerous charge even when unplugged. If you are not experienced with appliance repair, contact a qualified technician.

Steps to check the primary door switch and latch:

• 1. Inspect the door closure: Open and close the door several times. Ensure it closes firmly and evenly, with no sagging or resistance. If the door feels loose or misaligned, the latch hooks may not be engaging the switches correctly.
• 2. Check for obvious damage: Look at the plastic latch hooks on the door and the strike area on the cavity front. If any hook is cracked, bent, or worn, the switch may not actuate.
• 3. Access the control side panel: Remove the outer case (usually screws at the back and sides). Do not touch any metal parts near the high-voltage transformer or capacitor. Locate the door interlock switch cluster near the door latch assembly.
• 4. Test the primary switch: With the door closed, use a multimeter set to continuity or ohms across the primary switch terminals (usually COM and NO). It should read closed (near 0 Ω) when the door is closed and open when the door is open. If readings are inconsistent, the switch is faulty.
• 5. Check wiring and bracket: Ensure the spade connectors are tight on the switch terminals and the switch bracket is not bent or loose. Tighten screws if needed.
• 6. Replace if faulty: If the primary switch fails continuity tests or shows signs of heat damage or clicking inconsistency, replace it with a compatible Sage door interlock microswitch. Transfer wires one by one to the new switch.
• 7. Reassemble and test: Refit the outer cover, plug the unit back in, and test with a microwave-safe cup of water for 30–60 seconds. Confirm that the unit starts reliably.

If the unit still will not start, the issue may involve the secondary or monitor switch, or the control PCB, which should be checked by a professional.