I received a prompt response and excellent technical support for the remote diagnosis (Oxfordshire) and resolution of my GivEnergy EMS configuration. My GivEnergy issue involved a single inverter and battery that had a loss of calibration, a critical low voltage drop. It needed a recovery and re-calibration, and was supported via email into yesterday evening being resolved within 24 hours. Ron demonstrated a very high level of knowledge and experience in the intricacies of a GivEnergy EMS configuration, even surpassing the understanding of GivEnergy itself when it was still operational. I have already recommended their services to a neighbour as I’d be happy to use their services again based on the fair pricing and the quality of their support.
Fronius Isolation Fault — State 475 & 502 Earth Fault Diagnosis
- Not affiliated with Fronius
- No fix, no fee
- Covers state 475, 502 & 401
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.
Book your free remote diagnosticBack to Fronius hubIndependent — not affiliated with Fronius International.
What a fantastic service. Had my fault diagnosed within minutes and actually managed to resolve the issue remotely within a few minutes more. This guy is like a “Solar Batman” helping consumers fix their problems using his extensive industry knowledge and expertise. Outstanding service. Thank you so much.
Ron dealt with a battery issue within an hour on a weekend remotely. Very clear instructions to fix the issue worked first time. Excellent service.
Ronald was great to help me sort out my giv energy inverter issue since company has gone bankrupt in april 26.
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
⭐⭐⭐⭐⭐ 5-Star Review – Solar Tech Support Installing solar panels is only the first step! To get the best possible performance and maximise your investment, you need to make sure your system is configured correctly and all settings are properly optimised. **Solar Tech Support did exactly that for me, and I couldn't be happier with their professional service!** Their knowledge, expertise, and attention to detail helped me optimise my solar system to get the most out of it. If you already have solar panels and battery storage, I highly recommend contacting Solar Tech Support for professional advice, system optimisation, and technical support. Don't just install solar panels – make sure you're getting the maximum benefit from your investment! ⭐⭐⭐⭐⭐ Highly recommended! Thank you, Solar Tech Support, for your excellent service!
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.
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.
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.
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.
Understand the common fault locations
In order of frequency, the most common fault locations on UK Fronius installations are:
Corroded connectors also introduce electrical resistance, causing them to heat up under load. This is a fire risk as well as an insulation fault.
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 — 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.
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.
Isolation fault — common questions
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
- No fix, no fee
- On-site visits available
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Due to unprecedented demand we’re currently only carrying out on-site work in Yorkshire, and replies are taking up to 7 days. Remote diagnostics continue for the whole UK as normal.
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Got a solar fault or need a quick answer? Drop us a message and we usually reply within a few minutes. Mon–Fri, 9am–7pm.