Warning What does this mean?
Your system is down or running degraded, but this is not an immediate safety danger. Work through the safe steps below.
Solis Inverter UN-G-F Error — Grid Frequency Too Low
UN-G-F means the utility grid’s frequency dropped below your inverter’s protection limit, so the inverter disconnected itself. This is almost always a utility-side event rather than an inverter fault. Wait for the grid to stabilize — the inverter will reconnect on its own once conditions are normal.
What should I do first?
Two quick questions — we'll point you to the right starting point.
Is this code still showing on your inverter's display?
Is your system producing power right now?
What this code means
Your inverter can only feed power into a healthy grid, and “healthy” includes the frequency: 60 Hz in the US (50 Hz in many other regions). If the frequency sags too far below normal, something is wrong on the utility side — a generator tripping offline, a major load switching on, or a stressed grid during extreme weather.
UN-G-F — “under grid frequency” in Solis’s troubleshooting table — means the inverter measured the grid frequency below its trip threshold and disconnected to protect itself and to comply with grid rules. The manual’s grid-code settings show this trip point as a configurable protection value — for example, the under-frequency trip sits around 47.5 Hz on a 50 Hz system’s settings screen — a long way below normal, so it takes a genuine grid event to trigger it. The exact value on your system depends on the grid code your installer selected for your utility.
This is fundamentally different from an inverter fault. Your equipment is almost certainly fine; it is refusing to operate because the grid it must synchronize with is out of spec. The manual’s own remedy says the protection limit may only be adjusted through the user-defined grid function “if it’s allowed by electrical company” — in other words, the threshold is a utility matter, not a homeowner setting.
What is this downtime costing you?
Rough estimate while your system isn't producing. Adjust the numbers to match your setup.
≈ – kWh of lost production per day.
Estimate only — assumes ~80% real-world output vs. nameplate. Actual losses depend on weather, shading, panel direction, and your tariff.
Common causes
- A utility frequency excursion — the most common cause. A disturbance on the wider grid drags the frequency down, and every compliant inverter in the area trips off together.
- A local grid outage with a backup generator running — generators can drift off frequency, especially under heavy load, and the inverter will refuse to connect to them.
- An incorrect grid standard selected in the inverter settings — the wrong region’s limits make normal local frequency look like a fault. Only the installer can verify and correct this.
- A poor AC connection causing a bad frequency reading — a loose or degraded AC terminal can corrupt the measurement. This needs professional inspection.
Safe steps to try
Work top to bottom, ticking off each step as you complete it. 0 of 5 done.
Is your inverter still under warranty?
Before paying for a repair, check — your installer may fix this free.
Based on typical standard warranty terms — always confirm with your warranty card or installer paperwork, as terms vary by model, region, and purchase date.
When to call an electrician
Call your solar installer if UN-G-F persists while the grid is demonstrably normal — power on in the house, neighbors unaffected. That pattern points to a wrong grid-code setting, a faulty AC connection, or a failing measurement circuit, all of which need professional diagnosis. Never attempt to adjust the frequency protection limits yourself: the manual explicitly ties those settings to utility permission, and misconfigured grid protection can put utility workers at risk.
Frequently asked questions
Is my inverter broken?
Almost certainly not. UN-G-F is the inverter correctly responding to a bad grid, the way a smoke alarm correctly responds to smoke. If the code clears when the grid recovers, your inverter did exactly what it was designed to do.
How long before it reconnects?
The inverter watches the grid and reconnects automatically once the frequency has been back inside limits for a stable period — typically a few minutes. There is nothing to press or reset.
Can I adjust the frequency limit myself so this stops happening?
No. Those limits are set to match your utility’s grid code, and the manual says they may only be changed if the electrical company allows it. Widening them yourself could breach your interconnection agreement — leave grid settings to your installer and utility.
Why does this keep happening on hot afternoons?
Heat waves stress the grid: air conditioners max out demand while power plants and lines derate in the heat. Frequency dips during those peaks are a known grid phenomenon, and your inverter is simply riding them out as designed.
The power never went out, but I still got UN-G-F. Why?
Frequency can dip without a full outage — the lights stay on, but the 60 Hz wobbles. These events are usually brief and invisible except to equipment that measures frequency precisely, like your inverter.
Need a professional?
This fault may need professional diagnosis. Contact a qualified solar electrician in your area.
Sources: meaning and troubleshooting verified against the manufacturer's documentation — Solis S6-GC3P(37.5–60)K Installation and Operation Manual, Ver 1.0 (Ginlong Technologies, 2024), Table 8.1 Troubleshooting: UN-G-F01/02 — Under grid frequency; remedy: use user-defined function to adjust the protection limit only if allowed by electrical company; grid parameter setting screen shows the UN-G-F trip threshold as a configurable protection value.