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Fault code index · Fronius SnapINverter models

Fronius Fault Code Index

Every Fronius fault code and state code — what it means, the most likely cause, and what to do. Find your code in the index below or use the category sections to browse by system area.
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  • Fronius Primo, Symo, Eco and Symo Hybrid
  • Sourced from Fronius technical documentation
  • Status codes and warnings explained
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Ronald tried to help solve a fault with communications between battery and inverter. Whilst in the end a hardware fault was diagnosed and not possible to fix remotely his attempt to fix and guide me through steps to fault find were appreciated. He was available at a time convenient to my availability. Great service for anyone requiring independant tech support for their solar or battery system.

Ben Charlton · Jul 2026 Google

My solar panels stopped producing unexpectedly, contacted Ron who assisted me initially remotely and then visited to correctly diagnose that the problem was on the roof. Within a month the solar panels are now up and working, kept me up to date with when scaffolding arriving and the lads who checked the solar panels, a very professional team, organisation and service

Mr Andy Smith · Aug 2026 Trustpilot

My Givenergy system went offline, so I lost control of it. Ron from STS and Craig from Norfolk Solar were most helpful in diagnosing the problem by phone. Full marks for their patience and ability.

Tony Jackson · Jul 2026 Google

The Solar Tech Support company was the only one to respond to a request for someone to supply and fit a new inverter for our solar panels after our old one finally expired after 26 years. Ron kept us well informed throughout, came and ascertained that the issue was down to the inverter having failed then sourced and fitted a new one. He got the system up and running again, set up the wi-fi performance feedback and took away the old inverter for disposal. By acting promptly and fitting the job around existing commitments we were able to get our solar power unit back in operation with minimal delay in the short while before we were due to go away for a week. The work was carried out very professionally and we were asked to confirm that all was in order the following day. I was impressed that, having recently taken on additional work for GivEnergy customers we were able to keep our solar panel down-time to a minimum. I would highly recommend for prompt attention and first-rate service.

James Dignan · Aug 2026 Trustpilot

Wow... a firmware update to my inverter sent the whole system into meltdown – the battery discharged, and the house seemed to be drawing power, and the solar, who knows where that was going? Aghhh... A short email exchange with Roland and Solar Tech Support sorted the problem... the firmware had reversed a setting (from when it was installed), and the CT clamp needed to be reversed. As soon as I had done that, the world returned to normal. Thanks, Roland; there is no way I would have come to that conclusion. Would I recommend them? You bet! Worth the fee? You bet, again!

Pete Hawkins · Jul 2026 Google

Ron very quickly diagnosed what was wrong with my GivEnergy system. Unfortunately the kit has died after only 3.5 years of use-which is quite sad and timing couldn’t be worse with GivEnergy gone bust. Ron gave me advise on how to handle this with my installer. I’m hoping they’ll be forthcoming, but if they aren’t i now have a good idea how to deal with that. Thanks a lot Ron!

Dennis Koenen · Jul 2026 Google

Written by · Independent Solar Engineer Last updated

How to find your fault code. Fronius codes appear on the LED status lights on the inverter front panel. For detailed information, log into Fronius Solar.web → My Systems → [Device] → Events. The event log shows code numbers (STATE 102, STATE 307, etc.) with timestamps and descriptions. The inverter display shows codes with the STATE prefix; the Solar.web event log shows the bare number. Note the exact number before searching this index.

Routine state codes & warnings

Status codes that indicate normal operating conditions or warnings rather than hardware faults. The inverter either keeps operating or resumes by itself when conditions improve. The inverter display shows these with a STATE prefix; the Solar.web event log shows the bare number.

STATE 306Power low
There is not enough PV power available to feed energy into the grid, so the inverter pauses and repeats its startup routine. The official Fronius manual states that STATE 306 and STATE 307 appear routinely early in the morning and in the evening due to low light and do not indicate any kind of fault at those times. No restart is needed. If it stays on through bright midday sun, note when it occurs in the Solar.web event log and book a diagnosis.
STATE 307DC low
DC input voltage is too low for feeding energy into the grid. Treat it exactly like STATE 306: normal at dawn, dusk and in very dull or snowy conditions, clearing by itself when the light improves. If it persists in good daylight it can point to a string isolator left off, a disconnected string or severe shading. Do not open DC isolators or touch string wiring yourself.
STATE 509No energy fed into the grid in the past 24 hours
A warning rather than a hard fault: the inverter has exported nothing for 24 hours. Check whether the panels are covered with snow, and check the inverter's own DC rotary switch was not left off after roof or electrical work (turning that switch is fine, but do not open covers or touch wiring). Then look in the Solar.web event log for an earlier code that actually stopped generation, because STATE 509 is the symptom, not the cause. Hybrid systems show the companion code 520 for the PV side. Acknowledge the code; if generation does not resume in good daylight, book a diagnosis quoting the underlying code.
STATE 567Power derating caused by overvoltage
Grid voltage is running high, so the inverter is winding its output down to hold the voltage in range instead of disconnecting. This is grid-voltage-dependent power reduction (GVDPR), a country-setup feature that is not enabled on every unit; inverters without it trip to STATE 102 instead. The code clears automatically once grid voltage returns to the permissible range. Nothing is broken, but persistent derating means lost generation: record the times it appears in Solar.web, report a high-voltage concern to your DNO, and ask your installer to review AC cable sizing. Settings should only ever be altered to DNO-approved values.

Grid & AC faults

Status codes raised when the AC grid connection is outside permissible limits or an AC-side fault is detected. The inverter disconnects, keeps testing the grid, and resumes feeding in automatically once conditions are back within range.

STATE 102AC voltage too high
Grid voltage has risen above the permitted upper limit (around 253V in the UK) and the inverter has disconnected, as its G98/G99 protection settings require. It reconnects automatically once voltage is back in range. This is common on sunny middays in streets with a lot of solar exporting at once, and voltage rise on long AC cable runs makes it worse. Do not change the inverter's grid settings yourself. If it keeps recurring, note the dates and times in Solar.web and report a high-voltage concern to your DNO, who investigate supply voltage free of charge.
STATE 103AC voltage too low
Grid voltage has fallen below the permitted lower limit and the inverter has stopped feeding in. It is the low-voltage counterpart to STATE 102 above, and Fronius grades it Class 1: a momentary status caused by the public grid. After careful testing, and once grid conditions are within the permissible range again, the inverter resumes feeding energy into the grid by itself. Fronius's stated remedy is to check the grid connections, and to contact your system engineer if the code keeps recurring. Do not change the inverter's grid settings yourself.
STATE 107No AC grid
The inverter cannot detect a valid mains supply on its AC side, so it stays disconnected. Check whether the rest of the house has power, then check the solar circuit breaker at the consumer unit and the AC isolator near the inverter are ON. Resetting a tripped breaker once is fine; if it trips again, stop and call an electrician. After power returns, allow several minutes for the automatic reconnection delay before expecting generation. Never open the inverter or terminal covers.
STATE 301Overcurrent (AC)
The inverter has detected overcurrent on its AC output. Feed-in is briefly interrupted and the inverter repeats its startup routine, so a one-off event clears itself and needs no action. If the code keeps recurring, note the pattern in the Solar.web event log and contact a qualified engineer rather than repeatedly power-cycling the unit.

DC & Insulation faults

Status codes for DC-side overcurrent and insulation (earth-leakage) problems on the panel array or, on hybrid systems, the battery cabling. Insulation faults stop feed-in and must be treated as live-DC safety issues: never touch the array, DC cabling or connectors.

STATE 302Overcurrent (DC) or battery not detected
The inverter has detected overcurrent on the DC input, or on hybrid systems it cannot detect the battery. Feed-in is briefly interrupted and the inverter repeats its startup routine. On a hybrid system, check the battery is switched on and showing as connected in Solar.web. If the code is persistent, do not touch any DC or battery cabling; book a diagnosis with the event-log history to hand.
STATE 447 Insulation fault (PV or battery)
The insulation-resistance check has failed on the DC side and the inverter is not feeding any energy into the grid. The bracketed wording is from the hybrid manual; on PV-only Primo, Symo and Eco code lists it reads simply as an insulation fault. This is a possible earth fault on live DC wiring: do not touch the array, DC cabling or battery connections. The official manual says a permanently displayed code needs a Fronius-trained service engineer. Log whether it follows damp weather or is constant, and book a qualified engineer with that history to hand.
STATE 475 Insulation fault (solar panel to earth)
The pre-start insulation test has measured resistance between the panel array wiring and earth below the safe threshold, so the inverter refuses to feed in. Fronius service-partner guidance warns that metal parts not normally live may be energised while this code is present, so leave every DC component alone. Classic causes are water in MC4 connectors or module junction boxes (it often appears on damp mornings and clears as things dry out), chafed or rodent-damaged cable insulation, or a failed module. The manual says to contact your system engineer if the code keeps recurring; tracing it needs an insulation-resistance tester, string by string.
STATE 502Insulation fault on the solar modules or battery
A warning that the insulation measurement on the solar modules, or on the battery on hybrid systems, is below the expected level. The inverter shows the warning and continues to operate. Treat it the same way as the hard insulation faults: do not touch any DC cabling, note whether it tracks damp weather, and have a qualified engineer investigate if it keeps appearing.

Internal & thermal faults

Status codes originating inside the inverter: power-module overtemperature protection, a faulty temperature sensor, a stuck grid relay, or loss of communication with the power stage set.

STATE 303Overtemperature on the DC module
The DC-side power module has overheated and the inverter has interrupted feed-in to protect itself; it cools down and restarts automatically. Check the cooling vents are clear of dust and debris and that the inverter has free airflow with nothing stacked around it. If the code keeps recurring with good ventilation and normal ambient temperature, contact a qualified engineer.
STATE 304Overtemperature on the AC module
The AC-side power module has overheated and the inverter has interrupted feed-in until it cools. As with STATE 303, check ventilation: clear vents, free airflow, no direct heat source nearby. A one-off on a very hot day is not unusual; frequent repeats in normal conditions point to a cooling problem that needs an engineer to inspect.
STATE 401Cannot communicate with the power stage set
The inverter's control electronics cannot communicate with the power stage set, and the inverter will attempt to restart automatically. If the code is displayed all the time, do not keep power-cycling the unit. This is an internal hardware or firmware issue for a Fronius-trained service engineer, so book a diagnosis with the event-log history to hand.
STATE 406DC module temperature sensor faulty
The temperature sensor on the DC power module is giving an implausible reading, so the inverter cannot safely monitor its own temperature and stops feeding in. A restart will not fix a failed sensor. If the code is displayed permanently, it needs a Fronius-trained service engineer; there is nothing to check externally.
STATE 407Temperature sensor faulty
A temperature sensor inside the inverter has failed. The exact wording depends on the model: the Primo operating instructions call it an internal temperature sensor, while the Symo status-code list names the AC module temperature sensor, with 406 above covering the DC module. Fronius grades it Class 4 and states that the inverter will automatically attempt to connect again, which is what separates it from 406, where feed-in stops. A restart will not fix a failed sensor. Fronius's instruction is that if the status code is displayed all the time, notify a Fronius-trained service engineer. There is nothing to check externally.
STATE 457Grid relay sticking
The inverter's grid relay is stuck and the inverter is not feeding energy into the grid. The relay is the device that disconnects the inverter from the mains, so this is an internal hardware fault for a technician, not something to clear by repeated power-cycling. Book a qualified engineer with the Solar.web event-log history to hand, and do not open the inverter or its terminal covers.
Frequently asked questions
How often should I expect to see state codes on my Fronius? ↓
STATE 306 (Power low) and STATE 307 (DC low) are the codes you will see most often — both simply mean there is not yet enough sunlight to feed the grid, so they appear routinely at dawn and dusk and clear on their own as light levels rise. If a code outside that standby pair appears repeatedly in good daylight, note the number and check it against this index.
Why does my Fronius show STATE 102 even though my grid voltage seems normal? ↓
Grid voltage varies constantly — it may be at normal levels during off-peak times but spike above 253V during peak generation periods, especially with many solar systems exporting power. STATE 102 means the inverter measured AC voltage above the permitted limit and paused as a safety measure. Monitor how often it appears in your event log. If it's frequent, contact your DNO to investigate supply voltage in your area.
Can I read Fronius fault codes without logging into Solar.web? ↓
Yes — many faults show as LED codes on the inverter's front panel. However, for complete diagnostic information including timestamps and detailed descriptions, you'll need to log into Fronius Solar.web → My Systems → Events. This index will help you interpret both the LED codes and the event log entries.
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FAQ

Fronius fault code questions

Fronius codes show in two places: the LED status lights on the front panel, and the detailed event log in Fronius Solar.web (My Systems → your device → Events). The display shows codes with a STATE prefix (STATE 307, STATE 475); the Solar.web event log shows the bare number. Routine codes like STATE 306 and 307 at dawn and dusk are normal; insulation faults such as STATE 447 and 475 need action. Note the exact number before searching this index.
STATE 475 means the insulation test has failed between the solar panels and earth; STATE 447 is the same family of fault and also covers the battery side on hybrid systems. Treat both as a safety issue: the inverter stops feeding in, and metal parts that are not normally live may be energised, so do not touch any DC cabling, the panel array or the battery. If you want the system off, follow the safe shutdown guide rather than touching anything at the array. The usual causes are water ingress at DC connectors, damaged string-cable insulation, or a faulty panel junction box. Get a qualified engineer to inspect before any restart.
Routine codes like STATE 306, 307 and 567 clear automatically when conditions return to normal, so no restart is needed. Grid codes such as STATE 102 and 107 also clear themselves once the supply is back within limits. A power cycle (AC isolator off, 60 seconds, back on) can clear a one-off transient fault, but if the same code returns after a restart it's persistent and restarting won't fix it. Check this index to understand what the code indicates, then book a diagnosis.
No. STATE 306 (power low) and STATE 307 (DC low) just mean there isn't enough light to feed in. The official Fronius manual states they appear routinely early in the morning and in the evening and do not indicate any kind of fault. They clear automatically as the light improves. If either code stays on through bright midday sun, that is worth a diagnosis.
The remote diagnosis is free. We pull your full Solar.web event log to tell you what the code means and what's behind it. If it's something we can put right remotely — a setting or a grid-code check — it's £125, and you only pay if we fix it. A physical fault like a ground fault or a failed board is an on-site repair, quoted first, from £295.
Usually the same day. Send us the exact code (and whether a restart clears it) and we read your Solar.web history in a 30-minute remote session — you get a written summary of the cause and the recommended fix straight after. If the system has stopped producing entirely, flag that and we prioritise it.

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