Microwave will not start; display works, but pressing START does nothing or beeps three times and shows E01.

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.

• Check door closure: Ensure the Telefunken microwave door closes fully and the latch hooks engage firmly. Look for bent or damaged latch hooks or a warped door.
• Inspect door switches (interlock switches): Remove the outer cabinet (usually screws at the back and sides). Locate the door interlock switch cluster near the latch. Check that the switch actuators are properly engaged when the door is closed.
• Test switches with a multimeter: With the unit unplugged, disconnect each door switch (primary, secondary, and monitor switch if present) and test for continuity in the correct positions (NO/NC) according to markings. Replace any switch that does not change state when pressed.
• Check wiring harness: Inspect the small harness from the door switches to the control board for loose connectors, burnt pins, or broken wires. Reseat connectors firmly.
• Reassemble and test: Refit the cabinet, plug in, and test operation. If E01 persists, the control board door-sense circuit may be faulty and should be serviced by a professional.