What does GoodWe 'Isolation Failure' or 'ISO failure' mean?

Short answer

GoodWe 'Isolation Failure' means insulation resistance between the solar DC wiring and earth is too low, often due to damaged cable insulation, a poor earth connection or moisture on rainy mornings. The inverter won't feed in while it's present. Don't touch the panels or cables; tell your installer, who will test each string (DNS manual threshold: above 100 kΩ).