Quick answer
A SolarEdge isolation fault means the inverter has measured that the solar array is not properly isolated from ground — current may be leaking to ground somewhere in the array, its wiring, or the inverter. It’s a safety fault; SolarEdge says only a certified PV installer should fix the faulty string. It can clear and come back (sometimes on damp mornings), and it needs a qualified technician to find the cause.
An isolation fault can involve damaged wiring, moisture intrusion or other electrical problems that need professional testing to find. Renew Solar Services is authorized to service and repair SolarEdge systems and diagnoses isolation faults throughout Nassau and Suffolk County.
Which SolarEdge equipment shows this
The same fault appears under different codes depending on the inverter and its firmware:
| What you see | Equipment | Source |
|---|---|---|
| “Isolation Fault” with Error 25 | Single-phase inverters with CPU firmware 3.18xx or earlier | NA Troubleshooting Addendum |
“Isolation Fault” with code 2x19 | Single-phase inverters with CPU firmware 3.19xx or later (LCD) | Addendum; Isolation App Note |
18x86 in the SetApp status screen | Single-phase inverters commissioned with SetApp | Isolation App Note |
| Red LED blinking, green and blue off, after moving the switch to P for 2 seconds and releasing it | HD-Wave SetApp models (SE3000H–SE11400H-US) — this pattern means “isolation or RCD problem” | HD-Wave SetApp Installation Guide |
121 / 8x58 | Three-phase inverters | Addendum |
Codes on other SolarEdge products, or on other brands, can mean something different. The P-position LED check is a technician step; homeowners only need to read what the display or app already shows.
What SolarEdge says it means
SolarEdge inverters are transformer-less, so the DC side of the system is meant to stay isolated from ground. The inverter checks that isolation, and on single-phase models it reports a fault when the total combined isolation resistance falls below 600 kΩ. SolarEdge’s troubleshooting table describes the cause as the PV array not being properly isolated from ground.
Common causes (from SolarEdge’s documentation)
- Solar modules with defective insulation
- Unshielded wires
- Defective power optimizers
- A fault inside the inverter itself
SolarEdge notes the fault may disappear and then come back after a short time — especially when it’s caused by morning moisture. A fault that only shows up on damp mornings still has a physical cause that needs finding.
What to note before you call
- Write down exactly what you see: the code, the message, and the LED colors. Note the time of day and whether it happened after rain, dew or snow.
- Check whether it recurs. If the system resumes producing by midday and the fault returns on wet mornings, note it — that pattern is a useful clue for a technician. Moisture is one possible cause, not a confirmed one, until testing finds where the isolation is breaking down.
- Look at your monitoring app for when production stopped.
- Don’t switch the inverter off and on to try to clear it. Restarting a safety fault doesn’t fix the cause.
Do not open the inverter, the disconnect or any junction box, and don’t touch or unplug any wiring — SolarEdge warns that troubleshooting can involve hazardous voltage levels. SolarEdge’s own guidance to owners is not to attempt repairs on the inverter or optimizers without a SolarEdge-certified installer or electrician.
When to call a professional
Call a professional when the isolation fault:
- stays on, or keeps coming back;
- appears together with no production during sunny hours;
- shows up after roof work, storm damage or animal activity under the panels.
SolarEdge’s documentation says only a certified PV installer should fix the faulty string, and that troubleshooting can involve hazardous voltages and is for qualified personnel only. SolarEdge also advises troubleshooting the fault as soon as it occurs, before it disappears — so call while it’s showing.
How it’s usually repaired
A technician isolates the problem string by string, tests insulation, and then narrows it down to a module, a damaged cable or connector, a failed optimizer, or the inverter. The repair is whatever that test finds: replacing a damaged wire or connector, a failed optimizer, a defective module, or — if the fault is inside the inverter — the inverter. Finding the exact component first matters, because replacing parts on a guess doesn’t clear an isolation fault.
More SolarEdge help
How Renew Solar Services can help
Our licensed electricians test the system string by string to find where the isolation is breaking down — a panel, a damaged wire or connector, an optimizer or the inverter — repair or replace that part, and retest to confirm the isolation problem is resolved. Renew Solar Services is authorized to service and repair SolarEdge systems and serves homes across Nassau and Suffolk County.
Sources
SolarEdge, Troubleshooting SolarEdge Systems, Addendum (North America), MAN-01-00332-1.1 · SolarEdge, SolarEdge isolation fault troubleshooting, Application Note v1.10 (Oct 2024) · SolarEdge, Single Phase Inverter with HD-Wave Technology Installation Guide, MAN-01-00541-1.4 (Aug 2020) · SolarEdge, PV Production and System Issues. Last verified October 20, 2026.
