Microwave will not start; display works but pressing Start does nothing, sometimes accompanied by a brief relay click.

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

Step-by-step checks:

• Inspect the door: Open and close the door firmly. Check that the door sits evenly and the latch hooks fully engage in the cabinet.
• Check for play in the latch: Wiggle the plastic latch hooks on the door of your Neff microwave. If they are cracked or loose, the interlock switches may not actuate correctly.
• Access the interlock switches: Remove the outer cabinet (usually Torx or Phillips screws at the back and sides). Carefully lift the cover away.
• Locate the door switch cluster: On Neff built-in microwaves, the primary and secondary door switches are mounted on a metal or plastic bracket near the door latch opening.
• Test switches with a multimeter: Disconnect the microwave from power. Remove the wires from each switch. Set the meter to continuity or ohms. With the door closed, the primary and secondary switches should read closed (0 Ω). With the door open, they should read open (OL). Replace any switch that does not change state correctly.
• Inspect wiring: Check the small harness from the switches to the control board for burnt, loose, or broken connectors. Reseat any loose plugs.
• Reassemble and test: Refit the cabinet, restore power, and test operation.

When to stop: If the unit still will not start after switch replacement, the control board or safety relay may be faulty. At that point, contact a qualified Neff service technician.