Induction cooktop shows E3 and refuses to start heating on one or more zones.

Safety first: Switch off the circuit breaker before opening the terminal cover.

• Verify supply voltage: With a multimeter and the breaker ON, measure the voltage at the wall connection or junction box (performed only if you are qualified). Ensure it matches the rating plate of the Gram cooktop (e.g. 230 V single-phase or 400 V 2N~).
• Inspect terminal block: Turn power OFF. Remove the terminal cover on the cooktop. Check that the bridge links are installed according to the wiring diagram on the cooktop label and that all screws are tight.
• Look for heat damage: Signs of melting or discoloration on the terminal block indicate overheating. Replace the terminal block and any damaged wiring.
• Correct wiring: If phases or neutral are miswired, correct according to the Gram installation diagram. Re-secure the strain relief so the cable cannot pull on the terminals.
• Test again: Restore power and test. If E3 still appears and the supply is correct, the power module may have a defective voltage sensing circuit and should be replaced.

Warning: Mains voltage is lethal. If you are not trained to work on fixed wiring, contact a licensed electrician.