Fronius fault guides
Plain answers to the fault codes and alerts we see most often on solar systems, with what our own monitoring and service records show.
- Fronius state 107 no AC grid detected: what it means and what to do
Fronius state 107 "No AC grid detected" means the inverter is not producing because it cannot detect a stable AC grid. Fronius notes that 107 also shows if the grid was only temporarily absent, for example during a power failure or shutdown. Grid codes like this clear by themselves once the grid is back within limits; if 107 stays on while your home has power, Fronius advises contacting your installer.
- Fronius state 240/241 arc detection: what it means and what to do
Fronius state codes 240 to 243 mean the inverter's integrated arc detection has triggered. Fronius explains that the inverter detects and extinguishes serial arcs by switching off the power, and that the state code must be reset manually before it feeds power again. Fronius's advice to owners is to contact your installer to check the system, and that reset should come after the inspection, not before.
- Fronius state 307 or 306 PV voltage low: what it means and what to do
Fronius state 306 "PV POWER LOW" and 307 "PV VOLTAGE LOW" mean the panels are not supplying enough power or voltage for the inverter to feed the grid, so it pauses and returns to its startup phase. Fronius states that both codes appear naturally every morning and evening because of low sunlight and are not the result of a fault. They only need attention if they persist in good sunlight.
- Fronius state 475 insulation error: what it means and what to do
Fronius state 475 means the inverter's automatic insulation measurement found too low a resistance between the solar array and ground, so it stops feeding power to the grid. Code 502 is the warning version of the same problem, shown while the inverter keeps running. Fronius says there may be a problem with the panels or their cabling and that it often happens only in certain conditions such as rain; its advice is to contact your installer.
- Fronius state 509 no power fed in: what it means and what to do
Fronius state 509 means the inverter has fed no energy into the grid in the last 24 hours. Fronius explains that this happens when not enough power is available from the panels, for example when they are covered with snow, dirt or leaves. It is a warning that stays on the display until acknowledged, and Fronius advises watching for any other state codes, which usually point to the real cause.