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Fronius · Common problems & faults

Fronius common problems & faults

STS engineers diagnose and repair 4 common problems & faults on Fronius systems. Click any topic below for a full step-by-step guide, or book a free remote diagnostic and we'll tell you what the fix is. The WiFi is the exception: it's never remote work. If the WiFi still won't connect after the guide, we can set it up on site, from £195.
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Rated 5.0 on Google Read all 151 reviews

Absolutely fantastic experience, after months of being fobbed off with rubbish from the installer Ronald fixed my issues in a few hours, his attention to detail and his tenacity was amazing, not only did he go above and beyond but did not ask for payment i had to ask him how to pay. If you need a solar fix this company is brilliant

Richard Rodgers · Aug 2026 Google

Contacted Solar Tech about my Givenergy battery storage system that wasn't working. Battery status was "idle". Given the company Givenergy had gone bust, I need independent quality technical help. Very patient and clearly very knowledgeable about battery systems Ron diagnosed possible issues and suggested several possible remedies. Worked our way through them and fortunately it began to work. The fault was very specific and only an experienced engineer would have thought to check. Suffice to say I'll be back if I need independent support again. Lastly you only pay if there is a solution. Outstanding.

Mr P · Jun 2026 Trustpilot

We decided to treat ourselves to an upgrade to our existing solar system, and after a little searching, it became evident that Ron and his team provide the service and support we required. Decommissioning and recommissioning our new SunSynk Acure inverter and a wall-mounted Fogstar battery (which is of substantial size and weight compared to the original) was completed swiftly and competently. The installation was perfectly executed, and all upgraded paperwork for the increased battery export capacity was handled by Ron. I have no hesitation in recommending this team of support technicians to you.

iain donkin · Sep 2026 Trustpilot

What an absolute star. Ron went well beyond what i would have hoped for. His attention to detail was incredible, even making good the work of others.

Miles Gladson · Sep 2026 Google

Outstanding support, very detailed knowledge of the system and clarity on what was needed to fix it, no hesitation in recommending them to all.

Robert Grant · Jul 2026 Google

This is the second time I have used Solar tech first time a faulty Givenergy inverter, tried all sorts to get it going my last call was to Solar tech and yes they got me back up and running, today system went down again due to a firmeware update and Ron talked me through everything all whilst he was on someone’s roof sorting their system out. I would recommend this chap to every body that has problems with their system no matter what make..

Douglas Reid · Jul 2026 Trustpilot

Written by · Independent Solar Engineer Last updated

What actually goes wrong with Fronius inverters

Fronius inverters tell you what is wrong with a numbered state code, and the first digit tells you how serious it is. Codes in the 100s are grid trips that clear on their own, 300s are normal low-light messages, 400s are hardware or software faults, and 500s are notifications. The two faults that come up most on UK Primo and Symo units are the isolation fault (state 475 and 502), nearly always water getting into an MC4 connector or the rooftop DC isolator, and grid overvoltage (state 102), where the voltage at your property climbs past the 253 volt limit and the inverter has to disconnect.

State 102 is not an inverter fault; it is your local network, and the lasting fix usually comes from the DNO. An isolation fault is the opposite: a genuine safety shutdown that needs a proper inspection, not repeated restarts. And if Solar.web shows you offline, the system usually keeps running, so check the inverter's own screen; most often the Datamanager card has just lost its WiFi link, and our Solar.web offline guide takes you through reconnecting it. If it still won't connect, we set it up on site, from £195: we connect it to your WiFi, set up your router, including a separate 2.4 GHz network if it needs one, and check it's reporting.

Apart from the WiFi, we start every job by reading your Solar.web event log remotely to work out which of these you are actually dealing with. The diagnostic is free. No fix, no fee.

Common problems & faults

4 common problems & faults we cover

Each topic links through to an engineer-led step-by-step guide.

Grid Overvoltage — Frequency Fault & State 102

Your Fronius inverter is disconnecting because the grid voltage at your property exceeds 253 volts — the upper limit set by UK grid code G98.

See Grid Overvoltage

Isolation Fault — State 475 & 502 Earth Fault

Your Fronius inverter has shut down because it detected a drop in DC insulation resistance — a leakage path to earth somewhere in the solar…

See Isolation Fault

Solar.web offline or not updating — the fix

Your Fronius Solar.web portal shows the system as offline or the monitoring data has stopped updating. Free step-by-step guide.

See Solar.web offline or not updating

State Code Alarm — Inverter Error Codes

Your Fronius inverter is displaying a numbered state code — a status message telling you something abnormal has been detected.

See State Code Alarm
FAQ

Fronius fault questions answered

The first digit tells you. Codes starting 1 are grid trips: the inverter disconnected because voltage or frequency went outside limits, and it reconnects when conditions settle. Codes starting 3 are operational messages, usually low light at dawn and dusk. Codes starting 4 are hardware or software faults, the ones to take seriously, especially if they come back after a power cycle. Codes starting 5 are notifications that sit until acknowledged. Then check the pattern in Solar.web: a code that returns every day at the same time needs looking at.
Some can. Solar.web offline is usually WiFi configuration or Datamanager firmware, and our Solar.web offline guide takes you through both. WiFi isn't remote work: if the Datamanager still won't reconnect to your WiFi, we can set it up on site, from £195. Grid overvoltage (state 102) is a network problem, so the fix comes from your DNO, but we can configure export limitation remotely and put together the Solar.web evidence your complaint needs. Isolation faults (475 and 502) need someone on the roof with an insulation resistance tester, but we narrow the affected string first, so the visit is short.
The remote diagnostic is free. We review your Solar.web event log and production data, tell you what is wrong and what fixing it involves, and if we cannot fix it you pay nothing. Where the fix is remote work, such as setting up export limitation, you only pay if the fix works; on-site WiFi setup for a Datamanager that won't reconnect is from £195. Where it needs on-site work, like tracing an isolation fault, you get the likely fault location identified before anyone goes on the roof, so you are not paying for exploratory time.
Free remote diagnostic

Need a Fronius engineer?

Tell us what's happening with your Fronius system. Free remote diagnostic, no-fix-no-fee. Most configuration faults resolved during the 30-minute session. We don't set up or diagnose WiFi remotely or over the phone: it's quicker and more reliable done on site.

  • No fix, no fee covers remote fixes. On-site work is quoted in writing before we start.
  • Emergency response within 4 hours during business hours
  • Written report regardless of outcome

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