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Problem diagnosis · Fronius

Fronius Isolation Fault — State 475 & 502 Earth Fault Diagnosis

Your Fronius inverter has shut down because it detected a drop in DC insulation resistance — a leakage path to earth somewhere in the solar array wiring. This is the most common Fronius fault in the UK and is almost always caused by water ingress into connectors or the rooftop DC isolator. Do not repeatedly restart.
  • Not affiliated with Fronius
  • Free remote diagnostic · no fix, no fee
  • Covers state 475, 502 & 401
Isolation fault keeps returning?

If the fault clears in dry weather and returns when it rains, the water entry point needs to be found. We identify the affected string remotely from Solar.web data before an engineer attends site.

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Independent — not affiliated with Fronius International.

5.0
13 Trustpilot reviews
Trustpilot Google

I have a GivEnergy system consisting of two batteries, two inverters and a controlling EMS (Energy Management System) which has not worked since Nov 2025. After six months I discovered Solar Tech Support, reached out to them and Ron phoned me back – how often do you get that service? Could not be more helpful – worked directly with me over the phone, outside what I would call normal working hours. Lucid explanations and we were able to discuss the issues and history using camera and email history. As this was a very rare setup, Ron was able to access an EMS expert in the field to confirm the solution. One sunny day in, I am now only paying for standing charge and a few pence for spikes in grid consumption while battery catches up with house demand.

Ian · May 2026 Trustpilot

When my GivEnergy system had an issue, I was completely left without support and had honestly lost all hope. Thankfully, I searched online and found Ron, which completely turned things around. After sending him a message, he responded incredibly fast and called me to assure me that he would get the problem fixed. I really admire his dedicated, supportive nature and his determination to find a solution. With this kind of outstanding attitude and customer service, he has absolutely secured a future customer in me.

Sree · May 2026 Trustpilot

Ron want out of is way to help, nothing was to much. He was very thorough in what he did Very knowledgeable I would highly recommend Ron and his company He did a fantastic job for me. if you have any problems, he'll do his best to help you out and resolve your problem. I wouldn't hesitate to recommend them

Dennis Brown · May 2026 Trustpilot

Ron took me through a diagnostic to confirm my GivEnergy Inverter had a fault. A common one as it turns out with the AC Inverter. As GivEnergy is defunct there is no immediate fix, aside from sourcing 2nd hand replacement. It may be that a fix becomes available over the summer which would make a lot of GivEnergy customers happy (Again)

Tony Deacon · May 2026 Trustpilot

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026 Trustpilot

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026 Trustpilot

Contacted Solar Tech Support in desperation. After explaining the issues I had with my system a diagnosis was made and a solution proposed. Fantastic service, even contacted a manufacturer to arrange replacement parts for me. Great communications, explained all they were doing and what I had to do, clearly and precisly. Followed up to confirm all was ok. Excellent service.

Mr Machin · May 2026 Trustpilot

After GivEnergy went into liquidation, just my luck, my battery started playing up (internal board crashed). Contacted my installer - not interested! Found Solar tech support on a Google search. Sooo glad I found this company! Ron is extremely helpful and has plenty of experience. He soon confirmed what the fault was, and helped me to get my system up and running again. Now moved my GivEnergy account to Solar tech support, and will definitely use again if I have more issues. Unusual to find such a helpful company in these times, no morons reading scripts, just direct contact with the engineer.

Keith Ballard · Apr 2026 Trustpilot

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026 Trustpilot

Ron is a super star. Two months ago my GivEnergy battery failed a firmware upgrade leaving it a brick. My installer couldn't/wouldn't fix it. GivEnergy couldn't/wouldn't fix it. Then they went into administration and all hope was lost. A flurry of emails later and Ron had diagnosed the fault (failed USB flash drive, something I'd suspected) and talked me through resolving it. Two months of nothing resolved in about 3 hours. It's great to work with someone who pays attention to the details, knows that they're doing (not just following a script) and gets stuff sorted without a fuss or up-charging.

Christopher · Apr 2026 Trustpilot

I can add to the list of customers who had already 'given up' on GivEnergy due to their appalling customer service, and that was before they went into administration (their Trustpilot reviews don't lie!). So you can imagine my desperation when, having changed my ISP and my Inverter, predictably, proving to be the only device that didn't connect automatically to my new network, I found zero prospect of any customer support with GivEnergy having called in the administrators just five days earlier! The salvation came from Solar Tech Support. My IT advisor stumbled across their web site and some very helpful tips for beleaguered GivEnergy customers, as well as an offer to provide direct assistance. Nothing ventured, I decided to drop them an E-Mail, with very low expectations based on my experience of GivEnergy customer support. Within an hour Ron had responded with some pin point advice, and after a few exchanges of E-Mails he had nailed the problem, enabling the combined efforts of my IT advisor and solar installer to resolve it and reconnect my Inverter. Thank you Solar Tech Support, and Ron in particular, for coming to the aid of a deserted and despondent GivEnergy customer. Expert, razor sharp advice and first class customer service, even though I wasn't officially a customer.

customer · Apr 2026 Trustpilot

This company are a rare gem, I had a very unusual problem following a failed firmware upgrade on my GivEnergy kit. I then found out GivEnergy were in administration and had dismissed all their support staff! None of the usual fixes to try and restore my inverter comms would work, and I looked everywhere, forums, GivEnergy youtube support videos - even AI couldn't figure it out. My installer was talking about huge sums for system replacements, and being vague / evasive about if they'd even install replacement GivEnergy inverter. Enter Solar Tech Support, reassuring and knowledgeable from the very start, I've learnt loads about my solar system though the friendly chat while my engineer worked as he diagnosed the problem and figured out a fix procedure that I've not found anywhere else - amazing . If you need solar system repairs - especially if you like me have been left high and dry by GivEnergy, I cannot recommend this company enough. Give them a call.

Andy Thomas · Apr 2026 Trustpilot

I sent a message on their website regarding a problem I have on my Givenergy system. Although not supplied by Ronald, I thought it was worth an email. Within the hour on a Saturday, he phoned and we discussed the problem. He logged in remotely and gave excellent advice. I'm too far away for his on-site help but he did diagnose the problem and was happy also to chat through my thoughts about an upcoming solar/battery install I'm planning. Great bloke.... if only he was nearer!

Philip · Apr 2026 Trustpilot

I have a GivEnergy system consisting of two batteries, two inverters and a controlling EMS (Energy Management System) which has not worked since Nov 2025. After six months I discovered Solar Tech Support, reached out to them and Ron phoned me back – how often do you get that service? Could not be more helpful – worked directly with me over the phone, outside what I would call normal working hours. Lucid explanations and we were able to discuss the issues and history using camera and email history. As this was a very rare setup, Ron was able to access an EMS expert in the field to confirm the solution. One sunny day in, I am now only paying for standing charge and a few pence for spikes in grid consumption while battery catches up with house demand.

Ian · May 2026 Trustpilot

When my GivEnergy system had an issue, I was completely left without support and had honestly lost all hope. Thankfully, I searched online and found Ron, which completely turned things around. After sending him a message, he responded incredibly fast and called me to assure me that he would get the problem fixed. I really admire his dedicated, supportive nature and his determination to find a solution. With this kind of outstanding attitude and customer service, he has absolutely secured a future customer in me.

Sree · May 2026 Trustpilot

Ron want out of is way to help, nothing was to much. He was very thorough in what he did Very knowledgeable I would highly recommend Ron and his company He did a fantastic job for me. if you have any problems, he'll do his best to help you out and resolve your problem. I wouldn't hesitate to recommend them

Dennis Brown · May 2026 Trustpilot

Ron took me through a diagnostic to confirm my GivEnergy Inverter had a fault. A common one as it turns out with the AC Inverter. As GivEnergy is defunct there is no immediate fix, aside from sourcing 2nd hand replacement. It may be that a fix becomes available over the summer which would make a lot of GivEnergy customers happy (Again)

Tony Deacon · May 2026 Trustpilot

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026 Trustpilot

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026 Trustpilot

Contacted Solar Tech Support in desperation. After explaining the issues I had with my system a diagnosis was made and a solution proposed. Fantastic service, even contacted a manufacturer to arrange replacement parts for me. Great communications, explained all they were doing and what I had to do, clearly and precisly. Followed up to confirm all was ok. Excellent service.

Mr Machin · May 2026 Trustpilot

After GivEnergy went into liquidation, just my luck, my battery started playing up (internal board crashed). Contacted my installer - not interested! Found Solar tech support on a Google search. Sooo glad I found this company! Ron is extremely helpful and has plenty of experience. He soon confirmed what the fault was, and helped me to get my system up and running again. Now moved my GivEnergy account to Solar tech support, and will definitely use again if I have more issues. Unusual to find such a helpful company in these times, no morons reading scripts, just direct contact with the engineer.

Keith Ballard · Apr 2026 Trustpilot

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026 Trustpilot

Ron is a super star. Two months ago my GivEnergy battery failed a firmware upgrade leaving it a brick. My installer couldn't/wouldn't fix it. GivEnergy couldn't/wouldn't fix it. Then they went into administration and all hope was lost. A flurry of emails later and Ron had diagnosed the fault (failed USB flash drive, something I'd suspected) and talked me through resolving it. Two months of nothing resolved in about 3 hours. It's great to work with someone who pays attention to the details, knows that they're doing (not just following a script) and gets stuff sorted without a fuss or up-charging.

Christopher · Apr 2026 Trustpilot

I can add to the list of customers who had already 'given up' on GivEnergy due to their appalling customer service, and that was before they went into administration (their Trustpilot reviews don't lie!). So you can imagine my desperation when, having changed my ISP and my Inverter, predictably, proving to be the only device that didn't connect automatically to my new network, I found zero prospect of any customer support with GivEnergy having called in the administrators just five days earlier! The salvation came from Solar Tech Support. My IT advisor stumbled across their web site and some very helpful tips for beleaguered GivEnergy customers, as well as an offer to provide direct assistance. Nothing ventured, I decided to drop them an E-Mail, with very low expectations based on my experience of GivEnergy customer support. Within an hour Ron had responded with some pin point advice, and after a few exchanges of E-Mails he had nailed the problem, enabling the combined efforts of my IT advisor and solar installer to resolve it and reconnect my Inverter. Thank you Solar Tech Support, and Ron in particular, for coming to the aid of a deserted and despondent GivEnergy customer. Expert, razor sharp advice and first class customer service, even though I wasn't officially a customer.

customer · Apr 2026 Trustpilot

This company are a rare gem, I had a very unusual problem following a failed firmware upgrade on my GivEnergy kit. I then found out GivEnergy were in administration and had dismissed all their support staff! None of the usual fixes to try and restore my inverter comms would work, and I looked everywhere, forums, GivEnergy youtube support videos - even AI couldn't figure it out. My installer was talking about huge sums for system replacements, and being vague / evasive about if they'd even install replacement GivEnergy inverter. Enter Solar Tech Support, reassuring and knowledgeable from the very start, I've learnt loads about my solar system though the friendly chat while my engineer worked as he diagnosed the problem and figured out a fix procedure that I've not found anywhere else - amazing . If you need solar system repairs - especially if you like me have been left high and dry by GivEnergy, I cannot recommend this company enough. Give them a call.

Andy Thomas · Apr 2026 Trustpilot

I sent a message on their website regarding a problem I have on my Givenergy system. Although not supplied by Ronald, I thought it was worth an email. Within the hour on a Saturday, he phoned and we discussed the problem. He logged in remotely and gave excellent advice. I'm too far away for his on-site help but he did diagnose the problem and was happy also to chat through my thoughts about an upcoming solar/battery install I'm planning. Great bloke.... if only he was nearer!

Philip · Apr 2026 Trustpilot
⚠️

Safety warning. An isolation fault means there is a conductive path between the DC wiring and earth. Do not touch DC cables, MC4 connectors, or the inside of the inverter. DC voltage from the solar panels is present whenever there is daylight and cannot be switched off. Isolate the system at the consumer unit and do not restart until the fault has been investigated by a qualified engineer.

Diagnostics

6-step isolation fault diagnosis

Most Fronius isolation faults are caused by water ingress. The diagnostic path below identifies whether that is the case and what needs to happen next.

1

Identify your isolation fault state code

Fronius uses two main state codes for isolation faults. State 475 (DC insulation fault) means the inverter has detected low insulation resistance on the DC side — a leakage current path to earth exists somewhere in the array wiring. State 502 (isolation fault DC+ or DC- to earth) is a more specific detection identifying a direct fault between a DC conductor and earth.

Both codes trigger an immediate safety shutdown. Check the Solar.web event log or the inverter display for the exact code and timestamp. If the fault appeared during or shortly after rain, moisture ingress is the most likely cause.

2

Do not repeatedly restart the inverter

An isolation fault is a genuine safety event — the electrical insulation between the DC wiring and earth has dropped below the safe threshold. Repeatedly restarting the inverter does not fix the fault and may make the underlying damage worse by driving current through a compromised connection. If the fault clears temporarily in dry weather and returns when it rains, this confirms moisture ingress. The fault path is still present and will deteriorate over time. Leave the system off and arrange an inspection.

3

Check the weather pattern against the fault log

Open Solar.web and compare the fault timestamps against recent weather. Isolation faults that appear during rain, heavy dew, or high humidity and clear when conditions dry out are almost always caused by water entering a connector, junction box, or DC isolator on the roof. This is the single most common cause of Fronius isolation faults in the UK. The corrosion at the water entry point is progressive — even if the system runs in dry weather, the underlying damage is getting worse.

4

Understand the common fault locations

In order of frequency, the most common fault locations on UK Fronius installations are:

MC4 connectors — badly crimped, non-genuine fittings, or connectors not fully clicked together at installation allow rainwater in over years of exposure
Rooftop DC isolator — cheaper units where the seal degrades after a few years of UV exposure, allowing water onto the terminals
Panel junction box — cracked diode housing or failed gasket allows moisture onto the bypass diodes
Cable insulation — UV degradation, chafing against roof tiles or mounting rails, or rodent damage creating a bare conductor that contacts earthed metalwork

Corroded connectors also introduce electrical resistance, causing them to heat up under load. This is a fire risk as well as an insulation fault.

5

Isolate the system safely

Turn off the AC isolator at the consumer unit first, then the DC isolator below the inverter. If you can safely access the rooftop DC isolator, turn that off too. Do not open the inverter enclosure, disconnect DC cables, or touch MC4 connectors while there is daylight — DC voltage from the panels cannot be switched off.

A visual inspection of accessible cable runs from ground level may reveal obvious damage — melted plastic, scorch marks, or water dripping from a connector — but the definitive test requires a qualified engineer with an insulation resistance tester on the roof.

6

Book a professional insulation resistance test

The fault location is identified using an insulation resistance (Riso) test on each PV string with the inverter disconnected. A healthy string reads above 1 megohm; a faulted string reads significantly lower. The engineer then isolates individual sections to narrow down whether the fault is in the cabling, a specific connector, the DC isolator, or a panel junction box.

STS can review your Solar.web data remotely to identify which string is affected and when the fault pattern started before an engineer attends site — reducing diagnosis time and cost.

Why isolation faults are the most common Fronius problem in the UK

Fronius Primo and Symo inverters have been installed in the UK since 2012, making many systems 10 years old or more. Over that time, the DC wiring on the roof is exposed to continuous UV radiation, temperature cycling, wind-driven rain, and in some cases rodent or bird damage. The weak points are always the connections — MC4 connectors, the rooftop DC isolator, and panel junction boxes.

The UK climate is particularly hard on these components. Persistent damp, frequent temperature swings around freezing, and salt air in coastal areas all accelerate seal degradation and corrosion. A connector that was perfectly sealed at installation can develop a moisture path after 5 to 8 years of weathering. Once water enters, it corrodes the contact surfaces, reducing insulation resistance and introducing electrical resistance that causes heating under load.

This is why Fronius isolation faults typically appear as an intermittent pattern that worsens over time — short faults during rain that eventually become permanent as corrosion progresses. Early diagnosis when the fault is still intermittent is significantly cheaper than waiting until a connector has failed completely or caused secondary damage to the inverter.

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FAQ

Isolation fault — common questions

The most common cause is water ingress into MC4 connectors or the rooftop DC isolator. State 475 and 502 both indicate the insulation resistance between DC wiring and earth has dropped below the safe threshold. Other causes include UV-degraded cable insulation, rodent damage, cracked panel junction boxes, and corroded connections. The fault typically appears during rain and may clear in dry weather — but the underlying damage is still present and worsening.
Water provides a conductive path between a DC conductor and earth. When the moisture evaporates, the resistance rises again and the inverter restarts. This pattern confirms moisture ingress — the entry point needs to be found and repaired. Leaving it causes progressive corrosion at the fault location, increasing the risk of a DC arc fault or fire. The connectors, DC isolator, and junction boxes should be inspected.
You can visually inspect accessible cable runs from ground level for obvious damage, melted connectors, or scorch marks. However, the definitive diagnosis requires an insulation resistance test on each PV string with the inverter disconnected — this must be done on the roof with DC-rated tools by a qualified solar engineer. Do not open the inverter, disconnect DC cables, or touch MC4 connectors while there is daylight.
State 475 is a general DC insulation fault — the inverter has detected low insulation resistance during normal operation. State 502 is more specific, indicating a direct fault path between DC positive or DC negative and earth. Both trigger an immediate safety shutdown. The diagnosis process is the same: identify the affected string, isolate the system, and perform an insulation resistance test to locate the fault.
A remote diagnostic session identifies the affected string and likely fault location — free if we can't fix it. If the fault is a single degraded MC4 connector or a failed DC isolator, the on-site repair is typically straightforward. If the fault is in the cable insulation or a panel junction box, more extensive work may be needed. STS reviews your Solar.web data first to narrow down the fault before an engineer visits — this avoids paying for exploratory time on the roof.
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Isolation fault? Let us find the cause.

We review your Solar.web fault history and string data to identify the affected circuit and likely fault location — before anyone goes on the roof.

  • Not affiliated with Fronius
  • Free remote diagnostic · no fix, no fee
  • On-site visits available across Yorkshire

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