🔧 Vaillant
🔧 Viessmann
🔧 Protherm
🔧 Daikin
🔧 Panasonic & Mitsubishi
🔧 Fronius / GoodWe / Solax
🔧 Bosch / Siemens
🔧 AEG / Electrolux
🔧 LG & Samsung
🔧 DeLonghi / Philips / Krups
Technical Diagnostics & Fault Codes • Photovoltaics & Solar Inverters (Fronius, GoodWe, Solax, Huawei)
Solar Inverter Faults: State 307, 509, Isolation Fault, Grid Overvoltage – Error Code Meaning, Troubleshooting & Repair
Complete diagnostic table of the most common faults for Fronius / GoodWe / Solax (Photovoltaics & Solar Inverters (Fronius, GoodWe, Solax, Huawei)) with quick troubleshooting steps and links to replacement parts:
Error Code Reference Table for Fronius / GoodWe / Solax and step-by-step repair procedure:
| Error Code | Meaning / Fault Symptom | Most Common Cause & Repair Procedure |
|---|---|---|
| State 509 / Grid Overvoltage | Grid overvoltage (above 253 V) – inverter disconnected from grid | High grid voltage around midday; inspect terminal contact resistance in the distribution board and check the 10-minute average voltage setting. |
| Isolation Fault / ISO Error | Low PV array insulation resistance to ground (moisture inside MC4 connector) | Water ingress inside a rooftop MC4 connector or solar DC cable chafed against roof tiles/mounting rails (most common during morning dew). |
| BMS / Battery Low Voltage | Deep discharge of battery storage bank in winter | Trigger a grid Force Charge or inspect the battery fuse disconnector. |