Fronius Error Codes
Common Fronius State codes — including the Australian Volt-Watt and Volt-VAr grid-protection states — explained for owners and installers.
- Manufacturer
- Fronius
- Codes documented
- 30
- Source
- Fronius docs & field references
- Scope
- Reference only
An independent reference compiled by Solar Analytica from Fronius documentation and field sources. Fronius reports faults as numbered State codes on the display or in Solar.web — states 1–4 are normal start-up states, while a fault state shows a number in the hundreds. This covers the codes owners and installers see most often (Fronius defines 100+ in total, many internal/rare). The most common, State 102, is a grid issue — high network voltage — not a faulty inverter; don't let anyone sell you a new one to “fix” it. Safety note: insulation, earth, and DC-polarity faults are licensed-installer work, and for a DC over-voltage switch off the DC isolator first.
- 30 Fronius fault and alarm codes, documented in plain English.
- Compiled from manufacturer documentation — independent and not affiliated with Fronius.
- Codes involving DC/AC isolators, wiring or opening the unit are licensed-electrician work — when in doubt, call your installer.
30 of 30 codes
- 102
AC voltage too high
The grid voltage measured at the inverter is above the safe threshold, so it disconnects to protect itself. The single most common Fronius state.
What to do
This is almost always a network issue, not an inverter fault — your local grid voltage is running high. It self-restores when voltage drops. If it's frequent, contact your installer or network operator; Volt-Watt/protection settings may need review (see code 567), and the network may need to adjust the supply.
- 103
AC voltage too low
The grid voltage is below the inverter's acceptable range.
What to do
Usually self-restores when the grid returns to range. Check the AC connections/main switch; if it recurs, contact your installer or network operator.
- 105
AC frequency too high
The grid frequency is above the acceptable range.
What to do
Self-restores when the grid returns to normal. If frequent — common on a backup generator — contact your installer or network operator.
- 106
AC frequency too low
The grid frequency is below the acceptable range.
What to do
Self-restores when the grid returns to normal. If it recurs, contact your installer or network operator.
- 107
No AC grid / outside limits
No grid is available, or several grid parameters are out of range, so the inverter can't synchronise.
What to do
Check the AC main switch and that the grid is on. If the grid is present and it persists, have your installer check the connection and settings.
- 108
Stand-alone operation detected
The inverter detected an islanding condition (running disconnected from the grid).
What to do
Usually corrects automatically once the grid is stable. If it recurs, contact your installer.
- 112
RCMU error
An error in the residual-current monitoring unit (RCMU).
What to do
Restart the inverter. If it persists, contact your installer or a Fronius Service Partner.
- 301
Overcurrent (AC)
A momentary AC over-current inside the inverter.
What to do
Usually rectified automatically. If it shows continuously, notify a Fronius Service Partner.
- 302
Overcurrent (DC)
A momentary DC over-current inside the inverter.
What to do
Usually rectified automatically. If it shows continuously, notify a Fronius Service Partner.
- 303
DC module over-temperature
The DC power stage is too hot — usually blocked ventilation, high ambient temperature, or units mounted too close.
What to do
Clear the ventilation slots/heat sink, improve airflow, and keep the unit out of direct sun. If it recurs, contact your installer.
- 304
AC module over-temperature
The AC power stage is too hot — same causes as 303.
What to do
Clear the ventilation slots/heat sink, improve airflow, and keep the unit out of direct sun. If it recurs, contact your installer.
- 306 · POWER LOW
PV output too low
The intermediate-circuit voltage is too low to feed in — usually just low light.
What to do
Corrects automatically as irradiance rises. If it shows in good sunlight, check the panels aren't shaded/dirty, or contact your installer.
- 307 · DC LOW
DC input voltage too low
The DC input voltage is too low for grid feed-in.
What to do
Normal at sunrise and sunset. If it persists during the day, contact your installer to check the array.
- 309
DC input voltage MPPT 1 too high
The DC voltage on tracker 1 exceeds the inverter's maximum.
What to do
Switch off the DC isolator. The string likely has too many panels in series — your installer must re-check string sizing.
- 311
DC string polarity reversed
A DC string is wired with reversed polarity.
What to do
Switch off the DC isolator and have your installer correct the DC wiring polarity — don't do this on a live array.
- 313
DC input voltage MPPT 2 too high
The DC voltage on tracker 2 exceeds the inverter's maximum.
What to do
Switch off the DC isolator. The string likely has too many panels in series — your installer must re-check string sizing.
- 326 · 327
Fan error
A cooling-fan fault (fan 1 or fan 2).
What to do
Check the fan area for blockage. If the fan is faulty it needs replacement — contact your installer or a Fronius Service Partner.
- 425
No communication with power stage
The control can't communicate with the power-stage set.
What to do
Do an AC reset (toggle the breaker). If it continues, contact a Fronius Service Partner.
- 436
Board incompatibility
Functional incompatibility between PC boards (often after a component replacement).
What to do
Update the inverter firmware. If it persists, contact a Fronius Service Partner.
- 443
Intermediate-circuit voltage fault
The intermediate-circuit voltage is too low or asymmetric.
What to do
Restart once. If it persists, contact a Fronius Service Partner.
- 447
Insulation fault
An insulation fault in the inverter or PV array.
What to do
Often appears in wet weather and clears when dry. If it's continuous, have an installer check the array and cabling insulation — don't keep resetting it.
- 448
Neutral conductor not connected
The neutral wire is not connected.
What to do
This is an electrical wiring fault — have a licensed electrician or installer check the neutral connection.
- 450
Guard cannot be found
The safety guard module was not detected.
What to do
Restart once. If it persists, contact a Fronius Service Partner.
- 452
Processor communication error
A communication error between the inverter's processors.
What to do
Do an AC reset. If it shows continuously, contact a Fronius Service Partner.
- 463
Reversed AC polarity
The AC connector is inserted incorrectly or the phase is reversed.
What to do
An electrical wiring fault — have your installer or a Fronius Service Partner correct the AC connection.
- 502
Insulation error on the PV modules
An insulation fault between the array (DC+/DC−) and earth — frequently in damp or rainy weather.
What to do
If it clears when dry, moisture is getting in. An installer should check the panels, cabling, and MC4 connectors for water ingress or damage. If it persists in dry weather, it needs investigation — don't keep resetting it.
- 509
No feed-in for 24 hours
The inverter hasn't fed energy into the grid in the past 24 hours.
What to do
Check the panels aren't shaded, snow-covered, or dirty, and that there isn't another active fault. Normal for a brand-new install before commissioning. If it continues, contact your installer.
- 516
No communication with storage unit
The inverter can't communicate with the connected battery/storage unit.
What to do
Check the battery is powered on and its communication cabling is intact. If it persists, contact your installer or the battery supplier.
- 517
Power derating by temperature
The inverter is reducing output because it's too hot.
What to do
Clear the cooling openings and improve airflow; keep the unit out of direct sun. If it recurs, contact your installer.
- 567
Volt-Watt power reduction (GVDPR)
Grid-Voltage-Dependent Power Reduction (Volt-Watt mode) is active — the inverter is curtailing output because the grid voltage is high.
What to do
This is required behaviour under Australian standards, not a fault — acknowledge it. If it happens often, your network voltage is high; contact your installer or network operator, as it's reducing your generation.
Frequently asked
- Where do these Fronius fault codes come from?
- We compile them from publicly available Fronius inverter documentation and field references, then rewrite each entry in plain English. Solar Analytica is independent and not affiliated with Fronius.
- Can I clear these faults myself?
- Some clear automatically once conditions return to normal. Anything involving DC isolators, AC switches, wiring or opening the unit is licensed-electrician work — if in doubt, contact your installer rather than working on a live system.
- My exact code isn't listed — why not?
- Firmware and model variants differ, and manufacturers occasionally revise their codes. We document the most common ones; if yours isn't here, check your inverter's manual or ask your installer.
- How current is this reference?
- Last reviewed June 2026. We revise it when the underlying manufacturer documentation changes.
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